TRAVERSE CITY, MI (AP)-- A U.S.-Canadian agency says efforts to clean up the Great Lakes have yielded mixed results over the past 25 years and big problems remain.
The International Joint Commission advises both federal governments on issues affecting shared waterways. A report issued Tuesday focuses on progress since the Great Lakes Water Quality Agreement was updated in 1987.
It says some types of toxic pollution have declined, although concentrations of mercury have risen in some fish and consumption advisories remain in place.
Invasive species remain troublesome although no new invaders are believed to have reached the lakes in ship ballast water since 2006.
Among the biggest remaining concerns are toxic algae blooms caused by phosphorus runoff and shrinking ice cover that contributes to lower water levels.