Microsoft said the water leaving the underwater data center was only a fraction of a degree warmer than the ambient ocean water, and that a few meters downstream the temperature difference could no longer be measured. It also said the site was placed where persistent currents would disperse heat and avoid harmful local effects.

Marine heat waves have been observed to cause major disruption to marine ecosystems. The paper states that using ocean water for cooling during a marine heat wave can produce exit water at a high temperature that is dangerous to aquatic life, and that elevated outlet temperature from an underwater data center is unfriendly to marine life because it inhibits continued ocean oxygenation.

Results: A significant negative correlation was observed between temperature differentials, ambient temperature, and benthic abundance. Thermal discharge generally led to reduced benthic diversity and abundance, with occasional increases under low ambient temperatures. Discussion: Thermal discharges adversely impact marine benthic organisms by decreasing biodiversity and changing community structure, largely due to elevated temperatures and reduced oxygen levels. Cold discharges present unique challenges that require further research to fully understand their ecological impacts. The discharge of thermal and cold effluents carry significant implications for marine ecosystems, exerting considerable impacts on the growth and reproductive patterns of numerous species, as well as on the structure and composition of various communities, such as phytoplankton. This increase in temperature can harm benthic communities, potentially leading to habitat loss, decreased biodiversity indices, or even species extinction.

Natick engineers said the vessel consumes no water, does not heat up the water, and does not cause noise pollution for nearby sea life. The article also reports that Microsoft measured no heating of the marine environment beyond a few inches from the vessel and that nearby shrimp movements drowned out the underwater noise.

During the first 105-day test phase, only a minimal amount of heat was released into the ocean, and Microsoft monitored both heat output and noise. The piece says the project quickly attracted marine life, with fish nearby and crabs crawling over the structure.

This peer-reviewed article explains that if ocean water is used for underwater data-center cooling, the resulting outlet water has a higher temperature. It warns that the higher outlet temperature poses a risk to marine biodiversity because warmer water reduces oxygen availability, which can stress aquatic life.

Microsoft said the underwater datacenter was 'very quiet' and that in the first test phase the water in the immediate vicinity warmed by no more than one-thousandth of a degree Celsius. It added that a few meters away the data center was masked by ocean background sounds such as shrimp snapping.

The main impact of OTEC to the marine environment is related to the discharge plume (this volume can reach a few hundred cubic meters per second), its flow regime, and its trajectory. This plume can modify the availability of nutrients which, in turn, can favor eutrophication of the marine environment. The difference in temperature and nutrient content could increase primary production in the surrounding environment, resulting in decreased dissolved oxygen levels and the possible proliferation of harmful algal blooms (HAB), so it is crucial to evaluate the depth of the plume discharge and the subsequent stabilization. Giraud et al. carried out evaluations of the effects of discharges from OTEC plants in the Martinique Islands; they found a variation of more than 0.3 °C at 150 m, concluding that the discharge would modify the phytoplankton assembly in the deep maximum of chlorophyll on a local scale. Modifications of these factors would have a direct effect on the marine community. Notwithstanding, OTEC plume discharges could increase the frequency of these blooms, however, there are no studies that confirm this relationship.

Microsoft said Project Natick showed datacenters can be operated and kept cool without using freshwater resources that are vital to people, agriculture, and wildlife. This source supports the claim that the project emphasized reduced environmental impacts rather than documented harm to marine ecosystems.

The article notes that environmental risks are a present issue for marine infrastructure and quotes an expert saying that using a heat exchanger must be done carefully because it can heat seawater and affect life around it. It also says such projects should be located where there has long been human presence so as not to affect more pristine ecosystems as much.

Stratification combined with elevated temperatures significantly affected the phytoplankton abundance and community structure.[10] Elevated seawater temperatures decreased the chlorophyll-a concentrations by 34% and 63%, at the surface and bottom, respectively.[10] The elevated seawater temperature at the bottom might not be high enough to significantly affect the macrobenthos, but significantly affected the phytoplankton and zooplankton communities.[10] Because these communities serve as food for the macrobenthic community, their changes resulted in growth of the macrobenthos.[10] Furthermore, this effect induced macrobenthic community succession, resulting in decreased species diversity and increased dominance.[10]

Overall, the FES found that there would be a shift in benthic organisms and fishes as a result of the replacement of cold-water species with narrow temperature tolerance ranges and an increase in species able to tolerate a wide range of temperatures, especially in the area near the discharge where the plume contacts the bottom (estimated to be approximately 10 acres) prior to lifting to the surface as it moves offshore.[6] This resulted in a prediction that an increased number of warm-water-tolerant forms, indigenous to the general area, would occupy the habitat exposed to the plume.[6] The area exposed to the plume would also experience a reduction of as much as 10–20 acres of bull kelp and a reduction in the kelp canopy within the 4°F isotherm.[6] There was also the prediction that losses of red and black abalone may occur as a result of reductions in algal food species in more than half of the intertidal and subtidal zones in Diablo Cove.[6]

The article says underwater data centers have the potential to harm marine ecosystems, but more study is needed to weigh the impact. It cites concerns about thermal pollution, noise, vibration, and other negative impacts, while noting that responsible site selection and design could minimize heat gain and hot spots.

The article says one of the primary issues is localized thermal pollution: servers generate a lot of heat, and transferring that heat to surrounding seawater can alter temperature regimes and affect sensitive aquatic organisms, particularly in stratified or low-circulation environments. It adds that initial studies suggest limited impacts at small scales, but uncertainty remains about cumulative effects of large-scale deployments.

Data centers often discharge warm water back into local rivers or lakes after cooling their systems. This thermal pollution can raise the water temperature of the receiving body, stressing aquatic life that is sensitive to temperature changes. Higher temperatures reduce dissolved oxygen levels, which is critical for fish and other organisms. Changes in temperature can disrupt breeding cycles, migration patterns, and the overall balance of aquatic ecosystems. In severe cases, prolonged exposure to elevated temperatures can lead to fish kills, loss of species that require cooler waters, and a shift toward more heat-tolerant, often less desirable organisms such as certain algae.

Microsoft reported that the underwater Project Natick prototype was designed and tested with marine environmental monitoring. Reporting on the project said the study measured fish impacts and that, so far, the impact had been positive, with an increase in the fish population and no chemicals used in the heat-exchange process.

The piece summarizes environmental concerns from engineers and commentators, stating that submerged server clusters could create localized thermal plumes and ecosystem disruption. It does not present primary measurements, but it is relevant as secondary reporting that frames the alleged risk as a possible consequence of waste heat discharge.

After circulating through cooling systems, water may be discharged back into surface waters at higher temperatures. Warmer discharge water can reduce dissolved oxygen levels, stress fish and aquatic organisms, promote algal blooms, and cause long-term changes to aquatic ecosystems. Environmental organizations and researchers have warned that thermal discharges from cooling systems could harm ecosystems if not carefully managed. Potential impacts include fish kills, habitat degradation, and shifts in species composition. Effective management strategies suggested include limiting discharge temperatures, using cooling ponds or towers, and monitoring downstream ecological conditions.

The piece argues that claims that heat discharged from planned underwater modules will cause significant and irreversible warming are unfounded. It states that comparable underwater systems show only minor localized temperature increases, typically under 1–2°C at the outlet, that dissipate within a few meters because of ocean currents and the sea's heat capacity.

IEEE Spectrum reported that the environmental impact of underwater data centers remains unknown and that it is difficult to predict the effects of much larger deployments. It said the heat and sounds should avoid disturbing fish and other marine life near the seafloor, but larger underwater data farms could pose uncertain impacts.

Despite their potential, underwater data centers remain controversial.[4] Marine scientists warn that temperature increases in coastal waters can affect local ecosystems.[4] Many marine species rely on stable temperatures for breeding, feeding, and migration.[4] If large numbers of submerged facilities released heat into coastal waters, researchers fear this could create localized thermal pollution that alters biodiversity and affects marine food chains.[4]

On the flip side, underwater data centers have the potential to harm marine ecosystems, but Masanet said more study is needed to weigh the impact.[9] Masanet noted concerns over thermal pollution, noise and vibration, and other negative impacts on the underwater environment.[9] And with responsible site selection and design, Masanet said the heat gain and hot spots within the surrounding water could be minimized.[9]

The article says Project Natick used seawater running through an air-to-liquid heat exchanger and then back into the ocean, illustrating the basic mechanism by which heat is discharged. It frames the design as reducing municipal water demand rather than establishing a biological impact assessment.

The post claims that data centers in the ocean would mainly heat the water in their immediate vicinity and could create concentrated hotspots that significantly impact the surrounding biosphere. This is commentary rather than primary evidence, but it directly articulates the harm hypothesis behind the claim.

The deployment of submerged facilities in aquatic settings may have repercussions on local ecosystems.[12] Initial evaluations indicate that strategically located underwater pods can harmoniously coexist with marine organisms, especially when they are crafted to align with conservation initiatives.[12] Incorporated findings from a 2023 marine biodiversity study near Project Natick’s Scotland site, showing minimal disruption to local ecosystems after 18 months.[12] Underwater data centers are often viewed as environmentally sustainable; however, they may still endanger marine ecosystems.[12] The construction of these facilities can disturb local wildlife and ecosystems, especially if their design does not incorporate measures for marine life protection.[12]

The most profound and irreversible damage, however, comes from the cumulative thermal output of thousands of UDCs.[1] While the heat from a single data pod is easily dissipated, the concentration of hundreds of pods in designated “data reefs” creates significant thermal plumes.[1] The constant, low-grade warming of the surrounding water begins to alter the local ecosystem in ways that were not predicted by the initial, small-scale environmental impact assessments.[1] This gentle warming has several cascading effects: oxygen depletion, metabolic disruption, algal blooms, and the creation of localized “dead zones” on the seafloor.[1]

However, this innovation introduces potential risks for marine environments, including localized thermal plumes, ecosystem disruption, and contamination risk from structural failures. AI-driven data centers placed offshore could create heat plumes that alter local temperature gradients, with possible effects on plankton communities, fish behavior, and benthic habitats. These changes may not be immediately visible but could accumulate over time. The article notes that research is still emerging and calls for robust environmental impact assessments, continuous monitoring, and precautionary limits on deployment density to avoid unforeseen ecological tipping points.

This commentary says the surrounding water a few meters downstream of a Natick vessel would get only a few thousandths of a degree warmer at most, but that a long-term study might be needed to observe possible thermal pollution effects from submerged pods.

This general discussion argues that localized thermal changes in coastal waters can affect ecosystems, but it is not a primary source and provides no direct measurements for ocean-based data-center discharge. It is best treated as background commentary only.

Thermal pollution arises from the discharge of warmed cooling water into the surrounding marine environment.[7] Early operational data indicate a localised temperature rise of 1 to 2 degrees Celsius dissipating within metres of the discharge point—a modest impact at current scales.[7] However, extrapolation to large-scale deployment in thermally sensitive areas introduces meaningful risk for species that depend on narrow temperature ranges for reproductive and feeding behaviour.[7]

With that concern rising, many people naturally ask: “Will placing datacenters in the ocean add even more heat to an already stressed environment?” It’s a fair question — and the science gives a clear, reassuring answer: No.[8] The thermal impact of an ocean-based datacenter is so small that it becomes indistinguishable from natural variation.[8] Microsoft’s Project Natick Prototype 2, deployed off Scotland for 6 months, confirmed this directly: no measurable warming of surrounding ocean water and no ecological harm; marine life thrived, colonizing the exterior like an artificial reef.[8] Ocean-based datacenters do not meaningfully warm their surroundings; their heat output is negligible compared to natural forces, and marine ecosystems often benefit from the structure.[8]

In other non-tropical regions of the world, marine heat waves have been responsible for widespread loss of habitat-forming species, their distribution and the structure of their communities. Even relatively small, persistent increases in water temperature can cause major ecological shifts. Commenters discuss whether the additional heat from underwater data centers could contribute to or exacerbate such localized marine heat waves, particularly in semi-enclosed or low-circulation environments. They highlight that while the global ocean is vast, localized thermal inputs may still matter ecologically, depending on discharge temperature, volume, and local mixing conditions.

Absolutely, the thermal output from underwater data centers could potentially affect marine ecosystems by raising water temperatures.[11] If this method becomes widely adopted, it raises concerns about cumulative effects, especially if multiple nations implement similar projects.[11] While one region might manage the impact, the combined efforts of several countries could lead to significant environmental changes.[11]