Driving along the northeastern shore of the Salton Sea early last week, Doug Barnum noticed the water was a bright lime green. It was a signal of something invisible going on in the lakes depths that would soon have an all-too-visible effect. Barnum, a federal scientist, called state Fish and Game workers and warned them: "Be prepared for a fish kill; its going to happen."

In fact, it was already happening. By the next day the seas north shore was clogged with the corpses of more than 1 million tilapia, according to Fish and Game estimates. The fish had died of a lack of oxygen after high winds churned up the lake, causing a chemical reaction that sucked the oxygen out of the water and tinged it green.

It was the largest fish kill in at least four years at the Salton Sea. But officials said it was neither surprising nor particularly worrisome. More fish died because there were more of them — not because conditions in the lake had dramatically worsened this summer. Indeed, the tilapia population was the biggest in years, having rebounded from a plunge in the lakes overall fish numbers that purged three other species — croaker, sargo and corvina.

It is unclear why those species have disappeared, and why tilapia remain plentiful despite last weeks die-off. Jack Crayon, an associate biologist with the California Department of Fish and Game, said that fish routinely die in the Salton Sea as it grows ever saltier. The croaker, sargo and corvina may have been more sensitive to the rise in salinity than the tilapia.

"We have probably gotten close to the point where the high salinity is likely to suppress the ability of those marine species to come back," Crayon said. Along with intense heat, rising salinity is assured at the 35-mile-long desert lake southeast of Indio. Created by accident a century ago when the Colorado River broke out of an irrigation canal and flowed into an ancient lakebed below sea level, the Salton Sea continues to exist because its fed by drain water from the Imperial Valleys sprawling farm operations.

The irrigation runoff is heavily seasoned with salt picked up from the soil. Every year, 4 million tons of salt are carried into the lake, which has no outlet. The water is 25% saltier than the ocean, making for a harsh environment. If nothing is done to stop the trend, the sea will get too salty for the tilapia, a commonly farmed fish that escaped into the lake in the 1970s from irrigation drains into which it had been released to clean out algae. If the tilapia disappear, there wont be food for fish-eating birds, including the threatened California brown pelican, which summers in a wildlife refuge at the lakes southern end.

The Salton Sea has evolved into a vital stopover on the Pacific Flyway, used by hundreds of thousands of birds a year, because of the reduction of much of Californias viable wetlands. Schemes to restore the lake, the largest in California, have been discussed for years. The state is about to release an environmental review of possible solutions, none of which would be simple or cheap.

Last weeks cleanup was much easier. At a boat launch in the Salton Sea State Recreation Area on the lakes northeastern shore, workers wearing Wellington boots shoveled dead fish into the bucket of a small tractor, which then carted the smelly load to a trash bin for transport to a landfill. By Saturday, many of the dead fish had sunk to the bottom of the lake and the bulk of the cleanup was over. State parks personnel were clearing harbor areas, but otherwise were letting nature do the work.

The air was heavy with the overripe, but bearable, scent of decay. The salty water and baking sun had mummified the fish carcasses washed up on the beach, so the scene was less one of rot than of a giant fish-drying operation. "This is basically a salted tilapia," Ranger Steven Bier said as he picked up a stiff, sandy body.

Summer is the slow season in the recreation area, when temperatures reach triple digits. Only fishermen and sun-loving tourists from northern Europe visiting nearby Joshua Tree and Anza-Borrego desert parks frequent it. The campgrounds were empty over the weekend, and Bier encountered only a few people on his Saturday-morning patrol.

The sight of one couple prompted him to fetch his camera from his pickup truck. They were casting fishing lines into the water at the end of a long beach lined with thousands of dead tilapia. They stood atop the crisp carcasses. Brian Aalberts and his wife, Beth, of Glendora had learned only Friday night of the fish kill, after they had already planned a day trip. They stuck with their itinerary and were reeling in live tilapia, though they threw them back because they were too small to keep.

Aalberts, who has fished the Salton Sea for years, was unfazed by the fish kill. "It doesnt bother me," he said. "Ive been out here before with fish die-offs. "I like the heat. I like the desolation," he added, explaining his attraction to the area. The lakes allure seemed less apparent to his wife, who was visiting for the first time. "It stinks," she said. "He said it smelled bad. But I didnt expect this." Bier made a point of telling visitors that the fish had died of a lack of oxygen, not from contamination. "Its an amazing place," he said later. "This is basically a biology textbook in real life."

Researchers have come to understand more about the sea in just the last two years, when San Diego State University scientists figured out that the lime color Barnum saw last week was a marker of conditions that lead to fish kills. When strong winds churn up the lake waters, the mixing releases hydrogen sulfide trapped in the lake bottom. The sulfide, a product of decomposing organic matter, combines with calcium in a chemical reaction that forms gypsum — the source of the green hue. But the reaction also strips oxygen from the water, leaving the fish without enough to live.

Barnum said computer modeling indicated that reducing the lakes size — as called for in some restoration plans — could make the problem worse. The winds building over a smaller sea with the same depth would generally be weaker and therefore less apt to turn over the water. As a result, the hydrogen sulfide would build to even greater levels in bottom sediments. But then, if a strong wind swept across the lake, it would free the bigger sulfide reserves, stripping so much oxygen from the water that virtually the entire aquatic food chain would expire. "Thats our big concern," Barnum said.
(By Bettina Boxall, Los Angeles Times, 07/08/2006)
http://www.latimes.com/news/science/environment/la-me-fish7aug07,1,4076258.story?track=rss