The level of radioactivity in the ocean varies depending on the location and depth of the water. In general, the concentration of radioactive isotopes in the ocean is relatively low, thanks to the vast volume of water and the dilution effect. Natural sources of radioactivity in the ocean include potassium-40, uranium-238, and thorium-232, which are present in seafloor sediments and dissolved in seawater. Cosmic rays also contribute to the radioactivity in the ocean's surface waters.

Human activities, such as nuclear weapon testing and nuclear accidents, have also released radioactive materials into the ocean. These include isotopes such as cesium-137 and strontium-90, which were released during the nuclear weapon tests in the 1950s and 1960s. The concentrations of these artificial radionuclides have generally declined over time, but they can still be detected in the ocean environment.

In areas near nuclear power plants or nuclear waste disposal sites, the levels of radioactivity in the ocean may be higher due to discharges or leaks of radioactive materials. However, strict regulations and monitoring are typically in place to minimize the impact of these activities on the marine environment. Overall, the ocean is considered to have relatively low levels of radioactivity compared to other environments, such as certain terrestrial ecosystems or nuclear waste storage facilities.