Except where water is drawn from deposits of highly radioactive minerals, its radioactivity from natural causes is usually low and of no immediate health significance. Pollution by radioactive wastes, however, may be highly dangerous. Radioactive material may be ingested directly through water supplies, but may also be present in more concentrated forms in fish, shellfish, or in plants irrigated with contaminated water< Artificial radioactive substances in water are derived from the fallout from nuclear testing, discharges from nuclear power reactors and reprocessing plants, and the disposal of radioactive wastes. The radionuclides of importance are strontium-90, caesium-137 and to some extent, iodine-131; but the concentrations of these radionuclides in drinking-water are normally very low. Radioactive contamination of reservoirs can result from underground explosions and nuclear fallout.
Nuclear contamination problems from the Russian Northern Fleet became known after the publication of the Report "The Russian Northern Fleet - Sources of Radioactive contamination" in mid 1990's, prepared by the Bellona Foundation. One of the authors Alexander Nikitin was arrested after its publication and charged with treason.