"The immune system of the Great Lakes is weakened and it needs to be restored to prevent the ecological collapse of the lakes," said Andy Buchsbaum, director of the National Wildlife Federation's Great Lakes office.

The warning, in a report signed by about 75 of the region's aquatic specialists, was delivered as a U.S. administration task force prepared to release its strategy for nursing the ailing lakes back to health.

Advocates are putting pressure on the administration for major new spending on a wide-ranging effort to fix problems ranging from the exotic species invasion to severely polluted "hot spots." They are calling for $20 billion over 15 years, mostly from the U.S. government but also from states and local governments.

But the Environmental Protection Agency has signalled the restoration plan may have to rely on existing U,S, government money and programs, saying it already expects to spend $5 billion over the next 10 years on Great Lakes water quality projects.

The final version of the task force plan is scheduled for release Monday in Chicago.

U.S. Representative John Dingell a Michigan Democrat, said he urged EPA Administrator Stephen Johnson this week to come up with more funding.

"The bottom line is that we have had enough study and wasted enough time," Dingell said.

"We need to restore and protect this precious resource and it's going to take money to do it."

The scientific report issued Thursday also called for a comprehensive approach, saying piecemeal efforts to fix individual problems hadn't done the job.

The report mentioned a familiar litany of problems - sewage-fouled beaches, declining fish populations, fish tainted with toxins.

Many of the causes have been around for decades: overfishing, urban and agricultural runoff, toxic dumping. But the lakes are becoming steadily less capable of dealing with them, the report said.

That's because their "self-regulating mechanisms" such as wetlands, tributaries and connecting channels are falling apart, it said. Historically, they have served as buffers between the lakes and damaging human activities.

Coastal wetlands, for example, have filtered out contaminants such as phosphorus before they could reach the lakes. But they're steadily disappearing; more than 90 per cent of presettlement wetlands in the Lake Huron-Erie corridor have been destroyed for development.

"What we need to do is allow the Great Lakes to respond to those stresses in ways that ecosystems normally do," said Don Scavia, director of the Michigan Sea Grant program and one of the report's lead authors.

"Most ecosystems are naturally resilient to change. In the Great Lakes, we've eliminated or reduced that resilience."

Some locations have reached a "tipping point" where the environment goes downhill quickly and unexpectedly as nature's protective buffers fail, the report said.

Protecting and upgrading coastal wetlands and rivers that flow into the lakes should be "at the heart" of the restoration plan, said Buchsbaum, co-chairman of a coalition that advised government agencies working on the U.S. plan.

"This report suggests you can solve many of these problems at the same time if you focus on the buffering capacity of the Great Lakes," he said.