Dead ducks have been found at two more wastewater treatment plants in the metro area, although the die-offs appear to have declined significantly in the past two weeks.

Wildlife scientists still can't pin down what's driving the malnourishment and loss of waterproofing that is causing the ducks to die from hypothermia.

More than 600 ducks have been collected from several metro-area sites since early January, when workers at the Metro Wastewater plant in northeast Denver reported finding the dead birds.

In the past two weeks, new reports of dead ducks have come from Boulder's wastewater facility and the Littleton-Englewood plant. In total, five sites in the region have reported significant duck die-offs. Four of those were at or near wastewater treatment plants.

Test results don't point to a specific cause for the problem, and the ducks show no signs of disease, the Colorado Division of Wildlife said Friday.

Labs operated by the U.S. Fish and Wildlife Service in Ashland, Ore., and the U.S. Geological Survey in Madison, Wis., are conducting further tests, the DOW said.

hartmant@RockyMountainNews.com or 303-954-5048