The $5.5 million project in the lake east of Roseburg targets an estimated 90 million tui chub that have altered the environmental balance of the popular fishing lake, creating toxic blooms of algae during the summer that have closed the lake at times to most recreational use.

A gate will open at the north end of the 3,000-acre lake, eventually dropping the level 8 feet from its 50-foot depth and shrinking the lake to 2,600 acres.

In September 65 tons of rotenone, a poison, will be added, killing all fish and aquatic life.

The lake will be restocked with trout in 2007.

About one half of the fish will sink, the other half will float in what is likely to be a smelly, putrid kill-off.

The dead fish will be skimmed off and possibly used for fish fertilizer.

The once deep-blue waters of the mile-high lake have clouded in recent years as the chub proliferated.

Brought in as bait from the Klamath Basin, the chubs multiplied like locusts, elbowed out rainbow trout to the ratio of 200 to 1, dirtied the water and drove campers away.

Diamond Lake is one of the most popular year-round forest retreats in Oregon. Visitors can chose from some 500 campsites or Diamond Lake Lodge.

The Roseburg-based conservation group Umpqua Watersheds opposed the plan, likening it to treating Diamond Lake as if it were a bathtub to be drained and filled at will.

Some in the conservation community support the plan, as long as it is done carefully.

"They're stuck, because they got such a bio mess, and it becomes so putrid it's a health hazard, said Bill Bakke, executive director of Portland-based Native Fish Society. "Considering the situation, I do think it is the right thing to do."

Diamond Lake had no fish in it until the state stocked it with trout in 1910 to form a recreational fishery.

The tui chub was introduced in the mid-1900s, biologists think. The state lowered the lake and zapped it with rotenone in 1954 and thought the problem was solved.

But the fish showed up again in 1992.

Last summer a canal from the 1954 poisoning was excavated again.

The outlet was rebuilt and crews are installing a new headgate.

The lake will be lowered about 1 foot every four to six weeks.

The lake will be open for fishing again in April 2006, and the Diamond Lake Lodge will remain open year-round. The lake may be closed to the public briefly in September, when the rotenone is applied.

Rotenone breaks down quickly and will be non-detectable within three to four weeks. No water will be released until that time after the fish are killed to prevent problems downstream.

A commercial fishing firm will be hired to net as many fish as possible before the poisoning in September, then take out the dead fish.

(Copyright 2005 by The Associated Press. All Rights Reserved.)