TRAVERSE CITY, Mich. (AP) -- A decades-old effort to nurse the battered Great Lakes to health has made progress toward reducing toxic pollution and slamming the door on invasive species, but the freshwater seas continue to face serious threats, a U.S.-Canadian agency said Tuesday.
The International Joint Commission, which advises both nations on issues affecting shared waterways, said their governments had compiled a mixed record in restoring the Great Lakes, which for much of the 20th Century were fouled by industrial and household sewage and overrun with exotic fish and mussels.
Levels of some toxins have dropped, although the rate of decline has slowed and new chemicals have turned up, the commission said. Algae blooms were reduced dramatically, only to stage a frustrating comeback in recent years. Rising surface temperatures and shrinking winter ice cover are contributing to lower water levels, suggesting that the lakes' ecology may be linked increasingly to climate change.
The commission has provided regular progress reports since the U.S. and Canada signed the Great Lakes Water Quality Agreement in 1972, when the system containing one-fifth of the world's fresh water was notoriously dirty and Lake Erie was widely described as biologically dead.
The latest report card focuses on the period since 1987, when the pact was updated with an emphasis on reducing toxins and cleaning up 43 highly contaminated areas. The two nations signed another version last year.
"We've proved that when we put our minds to it, we can clean up the lakes," said Lana Pollack, chairwoman of the U.S. delegation to the commission. "When we take our eye off the ball, we go backward."
The analysis is based on a variety of chemical, biological and physical characteristics used to measure the lakes' well-being.
It says concentrations of most chemicals observed in key species such as herring gulls, walleye and mussels have declined, although the drop-offs occurred mostly between 1987 and 2000. But levels of newly arrived chemicals — including those used as flame retardants — rose during the same period. Mercury levels have remained stable or risen in popular sport fish, and consumption advisories remain in effect across the region.
A crackdown on phosphorus in laundry detergent and upgrades to wastewater treatment systems helped rein in runaway algae during the 1980s and 1990s. But stepped-up levels of a particular type of phosphorus, caused largely by fertilizer runoff from farmlands, have caused a sharp uptick in harmful blooms on Lake Erie and parts of the other lakes.
"I'm starting to see algae in places I've never seen it before," Pollack said, describing it as one problem that the Great Lakes region can solve on its own — in contrast to issues such as climate change and atmospheric deposits of mercury, which would require international cooperation.
One of the most serious challenges during the 25 years covered by the new report was a flood of invasive species such as zebra and quagga mussels, most of which arrived in ballast water dumped into Great Lakes harbors by oceangoing vessels. The mussels are blamed for clogging water intake pipes and unraveling food webs.
But no invaders are known to have hitchhiked to the lakes in ballast tanks since 2006, as both nations have imposed tougher standards for water disposal and treatment.
The U.S. has allocated more than $1 billion to an Obama administration program called the Great Lakes Restoration Initiative. It's designed to accelerate cleanups of toxic hot spots and prevent attacks by new invaders, including the feared Asian carp.
"Tight budgets on both sides of the border mean that cooperation and coordination of cleanup efforts are even more important," said Joe Comuzzi, chairman of the Canadian delegation to the commission.