The Conservation Law Foundation plans to sue ExxonMobil, accusing the oil company of polluting the Mystic River.

The environmental group's expected suit accuses ExxonMobil of contaminating the river with waste from its bulk storage facility in Everett, which the group says is not secure enough to prevent more pollutants from getting into the water.

The planned suit, which the oil giant was notified about on Tuesday, also is expected to allege that ExxonMobil failed to adequately protect the waterway from the effects of climate change.

Brad Campbell, president of the foundation, told WBUR's Bruce Gellerman on Monday the company should be held accountable for damage done to the river.

"ExxonMobil has filed essentially false statements to the government saying, 'We've done everything we could to prevent an unintended discharge of oil or hazardous substances,' " Campbell said. "That's simply not the case — their own science says it's not the case — and it's time ExxonMobil be held to account."

Campbell expressed concerns about rising water levels in the river, saying the Everett facility is not secure enough to stop future storms from causing oil and other hazardous waste to spread into the river and into Boston Harbor.

Alan Jeffers, a spokesman for ExxonMobil, said the company's Everett operations comply with federal and state environmental standards.

"They were recently inspected by both the EPA and the Massachusetts Department of Environmental Protection as part of their stormwater pollution prevention plan review," Jeffers told WBUR's Newscast Unit on Tuesday afternoon. "They found no issues with compliance or any cause for concern."

He also denied the foundation's accusations that ExxonMobil knew more about the damaging effects of climate change for years without disclosing information to the government, saying the company is focused on protecting all of its facilities from the potential impact of climate change.

"We design our facilities and build them to withstand a variety of extreme climatic and other conditions," Jeffers said.

The suit is expected to be filed within the next 60 days.