As the days grow longer and temperatures rise, green goo is multiplying somewhere in the shallower depths of Lake Hennessey -- the city of Napa's drinking supply.

While some algae growth is inevitable, reservoir regulators are hoping the bloom won't be big enough to warrant any algae-killing chemical treatments this year.

Last year no algae combatants were needed because the aquatic plant didn't reach dangerous levels, according to Phil Brun, general manager of the city's water division.

Besides sparing the drinking water another round of chemicals, the low algae count was a boon to the city for other reasons. Last year the water division was caught in a bind after a local environmental group, Earth Defense for the Environment Now, contested the health and safety of the use of copper sulfate -- the city's tried-and-true algaecide for Hennessey.

EDEN based its assertion on the fact that short-term exposure to copper can lead to gastrointestinal distress, and long-term exposure causes liver or kidney damage, according to the U.S. Environmental Protection Agency.

Like other heavy-impact pollutants, copper accumulates in higher and higher concentrations as it moves up the food chain, and eventually can lead to declines in fish and frog populations, according to several scientific studies.

In response to the environmentalists' concerns, the city's water officials started looking into an alternative algae-killer, PAK-27 -- a new chemical with potentially less environmental impacts, according to Brun.

But EDEN has since raised concerns about the PAK-27 solution precisely because it's an unknown quantity, according to EDEN spokeswoman Chris Malan.

"We have to hire experts, of course," Malan said. "Any kind of chemical in the watershed can be a problem but if we're going to protest anything we have to have experts to tell us what the impacts are."

She added that reviewing the city's environmental impact studies about PAK-27, which would satisfy the California Environmental Quality Act, could be a starting point to investigate the new algaecide, if and when the city files them.

"They didn't file CEQA documents on the copper sulfate," Malan said, pointing to the basis on which EDEN contested the city's use of copper sulfate in the first place.

Last year, when the city went to file a negative declaration for copper sulfate -- a document that would excuse them from conducting a full environmental impact study by stating that copper sulfate has little to no environmental impact -- EDEN protested. That's when the city halted its use of copper sulfate entirely, and the question of how to deal with the algae surfaced.

It has yet to be determined what the city's solution will be if and when Hennessey's algae gets to be too much.

In the past, EDEN has argued that the use of algae-killing chemicals in the reservoir is merely treating the symptom of the real problem, which they claim is excess nutrients in the lake.

A city-funded survey of the Lake Hennessey and Lake Milliken watersheds has identified vineyard run-off, particularly fertilizers and pesticides, as well as cattle grazing as likely sources of excess nutrients that are trickling into the lake and triggering algae growth.

Brun said trying to change existing land use practices can spark the timeless and often fruitless tug-of-war between private property owners and government agencies, but this isn't always the case.

So far Brun said the city's algae-fighting solution would be PAK-27 -- a sodium carbonate peroxyhydrate that breaks down into hydrogen peroxide and sodium carbonate when it hits water. Hydrogen peroxide has a half-life of less than eight hours in water, according to fact sheets from the California State Water Resources Control Board, which has permitted the use of the algaecide.

When EDEN questioned the city's ability to use PAK-27, Brun replied in an e-mail: "My understanding is that a CEQA analysis is not required for applications that are covered by the General Permit," adding that he believes PAK-27 was added to the city's permit in June 2006 for the discharge of aquatic pesticides for aquatic weed control in the lake.

Though EDEN's water expert, Nicole Beck, has voiced no issues about the use of PAK-27 in the short-term, she believes a long-term study is warranted.