After local environmentalists sounded the alarm on the city's use of copper sulfate to kill algae in Napa's main reservoir, water officials are switching to an alternative herbicide.

Members of Earth Defense for the Environment Now objected last spring to the city's application of copper sulfate to Lake Hennessey, citing the heavy metal's well-documented effects of decimating fish, frogs and other aquatic life. Like other heavy-impact pollutants, copper accumulates in higher concentrations as it moves up the food chain.

The group also protested the fact that the water division had not conducted a review of copper sulfate's environmental effects after the city asserted that the impact of a decade's worth of copper sulfate use was negligible. After EDEN contested that claim, the city stopped using copper sulfate, and has yet to decide whether it will resume, according to Phil Brun, general manager of the city's water division.

In the meantime, the city plans to try a new algaecide -- PAK-27 -- to eradicate the lake's green goo.

EDEN Director Chris Malan, remains skeptical about the city's switch to PAK-27, a hydrogen-peroxide based herbicide. She said relying on chemicals to kill algae is merely treating the symptom of the problem -- excess nutrients in the lake which spur algae growth in the first place.

"We're not familiar with PAK-27, but basically its hydrogen peroxide. So, OK, now we're not going to kill everything with copper, we'll use bleach," Malan said. "We're going to be checking out PAK-27. We want to understand now if (it is) something we want in the water supply."

Registered as a pesticide in 2004 with the Environmental Protection Agency, PAK-27 is almost 30 percent hydrogen peroxide and is designed to corrode away the unwanted algae.

A city-funded survey of the Lake Hennessey and Lake Milliken watersheds identified vineyard run-off, particularly fertilizers and pesticides, and 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 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.

He gave the example of an approximately $30,000 grant that helped Napa and Solano counties work with ranchers to fence cattle off from streams that were draining directly into an intake pump station in the delta.

"We may have these kinds of opportunities around Lake Hennessey and Milliken in the future, if and when the problem is identified to be large to devote those kind of funds and resources to," Brun said.

The city eliminated all cattle grazing from property adjacent to its reservoirs in the late 1990s.

Brun said only in recent years have water agencies, including Napa, begun assuming greater stewardship over not only the water supply but the surrounding watershed, as well.

"The industry trend is that source water protection and watershed management is something water utilities and water providers in general are paying more attention to," Brun said. "The industry is providing more training and information and we've been looking more closely into these issues in the past three to five years than we were 15 years ago."