California's State Water Resources Control Board has approved an ocean water restriction policy that will lead to the closure or modification of up to 19 coastal power plants.
The plants use ocean water to cool equipment and the policy seeks to reduce ocean water use by 93%, a move that could affect the plants' total capacity by 23,000MW, according to Reuters.
The power plants in question account for one third of the installed capacity of California, and would include two nuclear stations – the 2,150MW San Onofre nuclear station and the 2,240MW Diablo Canyon station.
A retrofit at two nuclear plants is expected to cost $7bn for the advanced technology needed to return 95% of adult fish unharmed to the sea at San Onofre's intake system.
The water board will require some power plants to comply within a year of the policy's approval.
Others will have a few years to carry out initiatives that demand 2020 modifications, replacements of older units and grid upgrades so that the plants can be closed permanently by that year.