A forthcoming report says millions of carp are actually protecting Utah Lake from massive dead zones as a result of giant algae blooms.

The report underscores the fact that cleaning up a damaged ecosystem is at best tricky -- and not without risk.

Naysayers critical of a massive and expensive cleanup effort now underway at Utah Lake have said that the lake is too far gone to save native species on the brink of extinction, and should be left for the many introduced species that now populate the waters.

But the forthcoming report shows that even the now-dominate non-native fish may be facing deadly challenges as the lake's ecosystem veers further off course.

For years the state has been working on a federally mandated report to assess two major pollutants -- phosphorus and mineral salts -- in Utah Lake. The final report is expected to be completed sometime in February, said Dave Wham of the Utah Division of Water Quality.

At 76.5 percent, sewer treatment plants discharge the largest portion of phosphorus that is poisoning the lake, largely from the shampoo, laundry detergent, soap and dish soap Utah Valley residents use every day.

Another 20.7 percent comes from streams, with 2.8 percent coming from groundwater, springs and drains, according to the report.

A preliminary evaluation and a draft report already total nearly 400 pages. The February report is not expected to differ significantly from the final draft, Wham said.

Local mayors and water managers have for years decried the report, saying it could force local sewage plants to spend millions to add phosphorus filters at taxpayer expense, and could even force a billion-dollar dredge of Utah Lake to clean it up.

While it is true that federal phosphorus reduction guidelines could be imposed on the cities around Utah Lake as a result of a pollution study now underway, the February report will not set any such limits. Instead it will call for at least several more years of study before a decision is made, Wham said.

It is possible that there is already so much phosphorus cycling in the lake that forcing cities to filter phosphorus would do no good at this point, Wham said. More study is needed.

A draft of the report says that Utah Lake is actually a phosphorus sink, meaning 214 tons of the phosphorus entering the lake every year never leaves, a damning revelation with long-reaching implications.

Once in the lake, that phosphorus is either trapped in lakebottom mud, or suspended in the water, where it acts as fertilizer, feeding "massive open-water cyanobacteria blooms in the late summer and fall," according to the report.

In many other lakes, such blooms and their aftermath kill fish and poison mammals that drink the water -- but Utah Lake has not had such problems yet.

That, according to the report, is because wind and carp stir up the lake bottom mud, making the water cloudy enough to prevent sunlight filtration, thus keeping blooms from growing to lethal proportions.

Among the wildlife relying on the lake are 226 species of birds, 49 mammalian species, 16 amphibians, and 18 species of fish, according to the report.

So while everyone agrees the carp are doing enormous environmental damage to the lake, they may also be saving it -- for now.

In order to return Utah Lake to something resembling its natural condition, and save the June sucker, one of the most endangered fish in the world, 7.5 million adult carp must be removed from Utah Lake, according to lake managers, and a major effort is now underway to do just that.

Bottom feeders that spend all day rooting up the lake bed, carp have destroyed most of the natural vegetation that once provided shelter for young June suckers and other native fish, as well as filtered and clarified sediment from the water.

With an average of 120 days each year when it is safe to fish, managers must remove 46,000 pounds of fish per day -- each fish weighing an average of 5.8 pounds -- in order to remove 1 million carp a year for seven years.

But removing the carp could backfire, officials admit, cleaning up the turbid waters just enough for algae blooms to explode to lethal levels.

"There is some uncertainty and some have questioned it," said Reed Harris of the June sucker recovery program, which is heading the carp removal effort. "If, (after the results) we have to look back and take another step or two, we will."

The hope is that, rather than causing algal blooms, removing the carp will allow the lakebottom to settle, trapping more phosphorus, he said.

With the carp gone, no one can say how much of the phosphorus trapped in the mud will be stirred up by wind and storms, and whether that same stirring will be enough to continue to keep the lake turbid enough to fend off deadly algal blooms -- but many are waiting to see what happens.

"We are interested in seeing how the carp removal process is going to proceed because that could potentially reset the lake ecosystem," Wham said.

"Hopefully the positive affects of the removal of the carp will more than make up for any negative impact," Harris said.

Warming waters

Another hazard is also affecting the lake and its ecosystem, according to the report. At most test sites in the lake, "a gradual increase in water temperatures was observed from 1991 to 2003," the latest available data, according to the report. "...The observed increase was most likely a result of lower stream flows, lake levels and elevated air temperatures."

Rising water temperatures hold less oxygen, encourage algal blooms, and can spell doom for fish spawn, according to the report.

"Summer water temperatures routinely exceed the preferred spawning temperatures for black crappie and large- and small-mouth bass at most in-lake and tributary (river) sampling locations in July," states the report.

In addition, water temperatures near the "upper range" for black bullhead were observed June through August, and for bluegill and green sunfish May through September.

"While water quality conditions are definitely not ideal in some areas of the lake at certain times, such conditions do not occur long enough to be fatal to fish populations," states the report.

The report also states that "habitat with adequate cover for young is a concern for all species" but notes that "conditions in a number of tributary streams have improved dramatically over the last 10 years" thanks to expensive and ongoing rehabilitation efforts.

Utah Lake's wetlands are "recognized locally and nationally for their critical importance to fish and wildlife," according to the report, but whatever the results of the report, no mandates will fall on local cities to try to reverse temperature trends, Wham said, noting information on temperature and its affects on the lake is coincidental and not a focus of federal or state study.

"It is kind of a nonissue for us because there is not a lot you can do about it on a big, shallow lake," he said.

Salt pollution

In addition to the threats of phosphorus and warming water, the report studied the effects of salt pollution in the lake, and this time, humans are not to blame.

Streams, "particularly the Provo River and Spanish Fork River" contribute 43 percent of the salts in the lake, with 26 percent coming from springs, and the rest from groundwater, sewage and other sources, according to the report.

High salinity in irrigation water makes it hard for roots to extract water from soil and can be lethal to irrigated crops, according to the report.

The "average response of all crops irrigated with Utah Lake water shows a 1 percent yield reduction due to salinity," fluctuating from 0.5 to 2.5 depending on the crop type, according to the report.

Onions, orchards and corn are most affected by the increasingly salty water, but the problem may be minimized by disappearing farms.

Today there are no acres of onions irrigated with Utah Lake water, and only 247 acres of orchards and 1,276 acres of corn, according to the report.

Provo River totals 36 percent of the water flowing into Utah Lake, followed by Spanish Fork River at 24 percent, Benjamin Slough at 9 percent, Mill Race Creek at 8 percent, Powell Slough at 6 percent, and Hobble Creek at 5 percent, with remaining inflows coming from rain, groundwater and springs.

Fifty-one percent of the water in the lake exits through Jordan River, 42 percent through evaporation and 7 percent seeps into ground water.

To read the evaluation and draft report on Utah Lake, visit www.waterquality.utah.gov/TMDL/ and scroll down to the Utah Lake section of "In-Progress TMDL Water Quality Studies."

During lawn watering season, water leaving the lake is below the salt threshold that affects turf, making it safe for lawns, according to the report. Gardeners using Utah Lake water can expect to lose less than 3 percent of their crop due to salt pollution.