The mysterious onset of an algae bloom along the Poudre River west of Fort Collins earlier this summer remains just that — a mystery.
“It’s probably a response to some nutrient loading,” Division of Wildlife area biologist Kurt Davies said of a green deposit along the river rocks that befuddled anglers and, perhaps, had a negative impact on fishing.
Davies identified it as a filamentous form of algae and speculated that the origin might be a ruptured septic tank of one of the numerous cabins in the area above Big Bend Campground.
Jamie Anthony, DOW’s water-quality coordinator, made a later trip up the river after runoff had subsided, finding the same general point of origin, but a greatly diminished amount of algae.
“The encouraging part is that I could see dry algae up on the rocks above the high-water mark,” Anthony said of the impact on the upper reaches.
Anthony found a greater amount of living green algae farther downstream around The Narrows.
“I could see a little bit, but not so dramatic as it was earlier. When Kurt made his original report, it was densest around Big Bend. Now it seems to have cycled out, with more green the farther you move downstream.”
The densest deposits remain around Indian Meadows, Anthony said.
Anthony remains unsure as to the origin, expressing hope this might be an isolated incident that might not return next year. When he measured the pH factor, he found levels were neutral, not dangerous to fish.
Davies said he had no way to judge the impact on fish until he completes his scheduled annual sampling in October.
Meanwhile, any health concerns are outside the realm of the wildlife agency.
“That’s under the purview of the Colorado Department of Health,” Davies said. “We informed them of the situation.”
Fishermen have delivered conflicting reports along the river, some blaming the algae for lagging catches, while others tell of success as usual.
Charlie Meyers: 303-954-1609 or cmeyers@denverpost.com
