CARLSBAD -- Scientists leading the effort to wipe out a dreaded noxious seaweed dubbed the "killer algae" said Tuesday they're cautiously optimistic they'll be able to declare victory at Agua Hedionda Lagoon and at Huntington Harbor in Orange County by the end of this year.

"I'm crossing my fingers," said Lars Anderson, a U.S. Department of Agriculture scientist who has specialized in invasive species for more than 30 years.

Anderson and biologist Bill Paznokas of the state's Department of Fish and Game said Tuesday that everything will depend on the outcome of lagoon-bottom surveys conducted this summer and fall.

"The next surveys are going to tell the tale," Paznokas said. "If we don't find anything this summer or fall, then we're going to declare eradication."

The discovery of the algae known as Caulerpa taxifolia in Agua Hedionda in June 1990 and a few months later at Huntington Harbor alarmed scientists up and down the state.

A tiny patch of the once-tropic, rapidly growing neon-green algae was found in the Mediterranean in 1984, and, left untreated, has spread to cover more than 10,000 acres of sea floor and doubling every year. The algae earned its nickname because as it spreads it smothers rock reefs and sandy sea bottom, killing off vegetation and killing or driving off fish and all other aquatic life.

The algae was once a popular saltwater aquarium plant, and Anderson said he suspects both Agua Hedionda and Huntington Harbor were infested by people dumping their aquarium tanks into the water.

At the Carlsbad lagoon and in Huntington Harbor, divers have been scouring the bottoms to find the plants, spreading tarps over those found, and pumping chlorine bleach underneath.

The techniques seem to have worked, said Anderson.

No Caulerpa has regrown from core samples taken from treated sections of lagoon bottom even under ideal conditions in his laboratory. Lagoon areas uncovered have also not produced any new growths of algae.

And surveys by divers have found no Caulerpa in Agua Hedionda since September 2002 or at Huntington Harbor since November 2002.

"Everything looks really good," Anderson said.

Anderson is a member of a team of scientists from the National Marine Fisheries Service, the San Diego and Santa Ana regional water quality control boards, state Fish and Game, and the federal Agriculture Department coordinating the extermination effort.

Even if victory is declared, scientists will continue to monitor the areas periodically, said Anderson and Paznokas, because even a microscopic particle left undetected could spawn a new outbreak.

"With any eradication program you have to make sure you've done your job," Paznokas said.

"The caveat," Anderson said, "is that we still have to do some periodic monitoring. You can't just walk away completely and not look back. But we will be well beyond the intense monitoring that we are doing now."

Anderson said the team is already working on a plan for surveillance of other high-risk areas in Southern California -- places with large populations and easy access to lagoons and the ocean -- to try to make sure there are no more infestations.

"We don't want to miss something that's out there already and we just don't know it," he said.

Contact staff writer Tim Mayer at (760) 901-4043 or tmayer@nctimes.com.