White Plains, N.Y. - The huge numbers of fish sucked to their death by the cooling system at the Indian Point nuclear plant prove that the system harms the Hudson River environment, a state official has ruled.

The finding by J. Jared Snyder, assistant commissioner of the Department of Environmental Conservation, is a victory for plant critics who claim that up to 1.2 billion fish and eggs are killed each year as the plant continuously draws in river water for use as a coolant.

"For decades, Indian Point has maintained that its cooling systems have no impact on Hudson River fish," said Robert Goldstein, general counsel to the environmental group Riverkeeper. "At long last, the DEC has pout an end to this fiction."

Snyder said that even the lowest estimate of fish deaths _ 900,000 annually _ "represents excessive fish kills" and establishes an adverse environmental impact.

The ruling, issued this month, means the plant's owner, Entergy Nuclear, may no longer raise the environmental-impact issue as it battles the state's order to build costly towers that recycle cooling water and make big river intakes unnecessary. Entergy had argued that the river's adult fish populations have been stable.

The towers, known as closed-cycle cooling, could cost Entergy more than $1.6 billion.

Company spokesman Jim Steets said Monday that Entergy will continue to argue against the towers, using several other issues that Snyder said can be raised at hearings that will start next year. Those issues include whether cooling towers are the best available technology for the money, the visual impact of the towers and the effect of outages that might be caused by construction.

"This ruling actually gives us the opportunity to bring in the argument that this could impact electric power reliability in New York, that the actual construction challenges may make it unfeasible," Steets said. "We still have to determine if building cooling towers is in the public interest."

A list provided by the Nuclear Regulatory Commission shows that 40 of the nation's nuclear power reactors use cooling towers, and nine of those also use bodies of water, including the Tennessee, Susquehanna and Connecticut rivers. The other 64 reactors, including the two at Indian Point, use only bodies of water, including Chesapeake Bay, the Mississippi River, two of the Great Lakes and the Atlantic and Pacific oceans.

The biggest cooling towers are 500 feet high and 400 feet in diameter at the base, the NRC said.

In May, Riverkeeper commissioned a report that studied 13 species of Hudson River fish and said 10 had suffered population declines since the mid-1970s. The report suggested a variety of causes including overfishing, global warming and invasive zebra mussels, but also blamed power plants, including Indian Point. At the time, Entergy disputed the study's findings and said the river's fish were "healthy and abundant."

Steets said then that by using screens, Indian Point safely returns most adult fish to the river; most eggs, he said, are fated to die anyway.

Entergy is seeking license extensions for the Indian Point reactors that would keep them running into the 2030s. The licenses expire in 2013 and 2015. If new cooling technology were imposed it would probably apply only if the licenses were extended.