The San Diego Regional Water Quality Control Board voted Wednesday not to renew water discharge permits for the South Bay Power Plant in Chula Vista.
Dynegy Energy operates the plant on the city's bayfront, on land owned by the Port of San Diego.
"Dynegy will not be allowed to discharge through this permit past December 2010," said Gabe Solmer with San Diego Coastkeeper.
She said the board's action confirms plans to dismantle the 50-year-old plant.
"Dynegy is in talks with the Port to dismantle the plant. Now those talks are ongoing and will continue," said Solmer.
San Diego Coastkeeper and other groups wanted the discharge permit ended as soon as next month.
Solmer said the South Bay Power Plant uses "once-through-cooling" - where water is sucked in from the sea and then discharged back into the ocean.
She said the process kills marine life and hurts the South San Diego Bay ecosystem.