Wonder about those chemicals in the river? Ask a bald eagle.

Eagles along the St. Croix National Scenic Riverway in Minnesota are showing scientists to what extent certain chemicals are polluting water, fish and small animals.

“They accumulate these contaminants in their system,” said the National Park Service’s Bill Route, who monitors and tests about 60 male-female eagle pairs from Apostle Island on Lake Superior south to where the St. Croix River enters the Mississippi River near Hastings, Minn. “If we can track those trends through time we can discover a good measure of human contaminants.”

The park service, drawing on the bald eagle research, is holding a series of six workshops this school year as a way to draw attention to the riverway as a learning laboratory through field work, observations, resource materials and lesson plan development.

The bald eagle workshop will include presentations by Route, who is director of the Park Service’s Great Lakes Inventory and Monitoring Network; Ted Gostomski, biologist and science writer for the network; and Rick Erickson, a science teacher at Bayfield High School in Wisconsin.

Scientists testing the eagles have found increasing evidence of two groups of flame retardants used in everything from textiles manufacturing to plastics in computer screens.

Blood samples taken from young bald eagles also show retardants once manufactured by 3M that were discovered a few years ago in Washington County, Route said.

The good news is that traces of the pesticide DDT, banned in 1972, continue to wane, he said. The pesticide was linked to a sharp population decline in bald eagles and peregrine falcons in the 1960s, he said.

“We need to congratulate ourselves for cleaning up the water with a lot of these pesticides,” he said. “We just have to be vigilant … to look for other chemicals.”

The St. Croix National Scenic Riverway, a unit of the NPS, oversees 255 miles of the St. Croix and Namekagon rivers.