CHICAGO – Congressional representatives and experts warned Monday that the world's largest surface freshwater system is under siege from a variety of threats and preservation efforts need more federal support.

U.S. Reps. Mark Kirk, Judy Biggert, Dan Lipinski and Peter Roskam of Illinois listened to testimony given by seven experts while critters in the Shedd Aquarium's invasive species exhibit lurked behind them.

Menaces to the lakes range from the stinky and obvious, such as sewage, to the more obscure, like a new invasive species called bloody red shrimp.

David Ullrich, executive director of the Great Lakes and St. Lawrence Cities Initiative, said he's most worried about sewage overflow.

A report issued by the Sierra Legal Defence Fund out of Canada last November found that more than 20 billion gallons of sewage were dumped into the Great Lakes in 2005 – including about 13 billion gallons from Detroit.

Kirk, who last year criticized Milwaukee for mistakenly discharging 800,000 gallons of partially treated sewage in Lake Michigan, said he hopes to pass legislation setting a federal deadline to outlaw dumping in the lakes.

"I'm concerned that other communities around the Great Lakes have not made the investments" some in Illinois have, Kirk said before the hearing began. "With 24 billion gallons of sewage going into the Great Lakes every year, it's simply something that the Congress needs to get involved with."

Panelists also expressed concern about the steady introduction of new species into the ecosystem, often through ballast water.

Stephen Brandt, the director of the Great Lakes Environmental Research Laboratory, in Ann Arbor, Mich., said there are more than 180 invasive species in the Great Lakes.

One of the newest invaders – the bloody red shrimp – was discovered about four months ago in Lake Michigan.

It's unclear what effect the shrimp will have on the region because there have only been several published scientific papers on the species, Brandt said.

The panelists and lawmakers also were worried about the prospect of invasion by the Asian carp, which are being prevented from entering Lake Michigan from the Mississippi River by a temporary barrier.

Biggert said legislators should authorize President Bush's $7.6 million request to complete the electronic barrier.

While Ullrich urged comprehensive Great Lakes restoration legislation, Roskam cautioned against "waiting for perfect."

"The 'perfect' is the enemy of the 'good,'" he said.