Ecologists concerned by Mirror Pond dredging plan

A Bend group’s plan to remove silt from Mirror Pond is being criticized by ecologists who say dredging the pond could harm water quality and aquatic animals.

The Oregon Department of State Lands has until the end of September to review a request from Mirror Pond Solutions, which wants to remove about 75,000 cubic yards of sediment from the pond. But groups, including the Oregon Department of Fish and Wildlife and the Upper Deschutes Watershed Council, contend this plan could worsen already poor water quality in the small lake between the dam at Newport Avenue and the former Colorado Avenue dam site.

“Whenever someone’s doing a big project on the river, we think water quality should be considered,” said Ryan Houston, executive director of the Upper Deschutes Watershed Council.

The pond, like much of the Deschutes River in Bend, already is too warm to be a good habitat for many fish. The longer water sits, the more it heats up, and dredging the pond would cause it to sit longer instead of encouraging a faster-moving channel that’s beginning to develop, Houston said.

“If anything, having a larger reservoir that could lead to warmer water could lead to more fish kills,” Houston said.

If Mirror Pond is left as is, Houston said, it likely would grow to resemble the area upstream of the Colorado Avenue bridge. That portion of the river used to be a pond but slowly filled in with wetlands.

“That is not an ecological disaster,” Houston said. “That is a healthier condition than if it were dredged.”

However, natural wetlands may not fit in Mirror Pond, a picturesque basin near downtown Bend that’s used to market the city to tourists. The majority of the comments Bend residents submitted to the Department of State Lands praised the proposed dredging for improving Mirror Pond’s appearance and recreational activities.

Any recreational uses should be balanced with preserving a habitat for aquatic animals, said Erik Moberly, a fish biologist with the Oregon Department of Fish and Wildlife.

“We’re advocates for fish and wildlife because they don’t have a voice for themselves,” Moberly said. “There’s got to be a balance between recreation and environmental stewardship.”

Any work should include adding riparian vegetation — plants that can live in permanently saturated soil — along the banks of the pond, he said.

This would be difficult to do for two reasons, Mirror Pond Solutions contractor Garry Sanders said. First, the land along the pond belongs to private landowners, and the group can’t force them to allow aquatic plants on their land.

Second, Mirror Pond has a reverse hydrology, which means water levels are highest during the summer growth period for sedges and rushes. This prevents them from growing and colonizing, Sanders said.

Moberly also was concerned about whether the dredging method would remove juvenile fish and other small organisms from the pond. Workers plan to use a suction device with a floating pipeline to pull water and sediment from the pond to a processing site, then tote the sediment away.

“If you’re just dredging out sediment from Mirror Pond, you would have to have a strong suction,” he said.

Suction dredges also create a disturbance in the water, encouraging animals to swim away, Sanders said.

“It’s triggering their fight-or-flight response, for the most part,” he said.

Most feedback from Bend residents has been positive, but in an online comment submitted to the Department of State Lands, Bend resident Mark Davis wrote that the suction dredging method would cause too much cloudiness caused by particles in the water. Bucket dredging, in which silt is scooped from the pond, would work better, he wrote.

“Please don’t let them muddy the waters of the Deschutes River for minimal benefits,” he wrote.

Davis, along with Moberly and Houston, expressed concerns about the Oregon spotted frog, a once-common animal listed as threatened under the Endangered Species Act in 2014. Mirror Pond was not designated as a critical habitat for the animal, said Bridget Moran, Bend field office supervisor with the U.S. Fish and Wildlife Service. The Bend office surveyed areas along the Deschutes River during the frog’s breeding season two years ago.

“We did a fairly exhaustive search of that in downtown Bend in 2015,” she said.

—  Reporter: 541-633-2160; jshumway@bendbulletin.com

Editor’s note: This article has been clarified. The original version did not make clear the concerns about the Oregon spotted Frog.