17. Farallon Islands (US)
The sea around the Farallon Islands off the coast of San Francisco was used as a dumping site for radioactive waste. An estimated 47,500 55-gallon steel drums were discarded here, but their exact location and the risk they pose to the environment is unclear. It is also believed that attempting to remove them would cause more damage than leaving them untouched. There is also an extensive elephant seal population, which attracts scores of great white sharks.
