Despite dozens of insidious invasive species, toxic chemicals that fall from the sky and rapidly rising water temperatures, Lake Superior's biggest threat may be the people who live along and visit its shores.
That was the consensus Monday from a panel of scientists gathered in Duluth for the largest-ever conference on the state of Lake Superior.
Several scientists told reporters that the world's largest freshwater lake is in generally good health but that pressures from humans -- development, pollution, rising temperatures and the movement of foreign species into the lake -- threaten the lake's cold, sensitive ecosystem.
"The biggest threat to Lake Superior is development along the shoreline ... more and more people pressure on the shore,'' said Deb Swackhamer, director of the University of Minnesota's Institute on the Environment and an expert on the effects of chemicals on freshwater ecosystems.
Swackhamer said most toxic pollutants in the lake have been declining in recent years, leading to a reduced impact on the ecosystem.
DDT and PCB levels in the lake have declined dramatically after the substances were banned, for example.
But human pressures on shore are increasing exponentially. It's in the near-shore areas most affected by land use where most of the lake's living organisms spend much of their time.
Mark Ebener, a fisheries biologist for the Chippewa-Ottawa Resource Authority in Sault Ste. Marie, Mich., said more people on more developed ground near the lake is helping speed runoff, causing erosion and destruction of habitat -- not just in the lake itself, but also in nearby tributaries. The same development brings leaky septic and wastewater systems that add fertilizer to the lake.
"The fish communities of the middle of Lake Superior are very healthy,'' he said, noting lake trout populations have recovered and are self-sustaining. "The part of the ecosystem that faces the most problems are the tributaries and near-shore areas'' such as wetlands, harbors, rivers and streams that lead into the lake.
While Ebener said that despite the introduction of invasive species into the Great Lakes -- such as sea lamprey, zebra mussels and now a fish-killing virus called VHS -- Ebener said human pressures are the most pressing problem that is not being addressed.
"The original invasive species is the problem. Us,'' Ebener quipped. "We are still the worst enemy of the aquatic community'' in the lake.
The Making a Great Lake Superior conference, under way through Wednesday at the Duluth Entertainment Convention Center, has attracted more than 450 scientists, natural resource managers, teachers, government officials, environmental group leaders and private citizens.
The conference has brought together national and international experts on the major ecological issues facing the lake, including rising water and air temperatures, invasive species, air and water pollution, fish populations, sewage overflows, rapid development on shore and more. The event also includes art exhibits and more events, some of which are open to the public.