Slow moving, but fast growing

A popular fishing pond has been overrun with snails, putting a damper on outdoor activities there for the foreseeable future.

The city of Post Falls announced Tuesday that Post Falls Park Pond is closed until further notice because of an infestation of Chinese mystery snails along the bank and bed of the pond.

"This is definitely not a native species," Post Falls Parks and Recreation Director Dave Fair said Monday.

The Post Falls Parks and Recreation Department and Avista are working together on management measures to remove the snails, the city announced Monday in a news release. Control options may include a range of mechanical, chemical or physical removal techniques during the remainder of the year.

In September 2021, the city addressed Eurasian watermilfoil and began working on the Asian mystery snails, Fair said.

"These guys are actually increasing," he said. "We’ve been told originally they fed on the milfoil. We figured that would get better. There’s not a lot of things that work on them, so we’re trying a lot of stuff."

The pond has been drained and winter runoff will be pumped out as crews work to manage the snail population. They have tried handpicking the snails out of the pond and letting winter run its course on the invasive species. Water may later be added to the pond to try chemical applications if necessary.

Fair said the snails are not harmful to humans or dogs, but they are incredibly invasive. He said crews have removed thousands of them in the past couple years.

"We’re so close to the river it’s real easy to have someone pick one up and drop it in the water," he said. "Definitely do not transport them."

The snails were most likely illegally introduced by people emptying aquariums into the pond. Abandoning pets and plants in ponds has significant negative impacts on native species and the use of facilities.

"We've seen a lot of things dumped into this pond," Fair said. "We’ve had pike, we see goldfish all the time, turtles."

The Idaho Department of Fish and Game will not stock the pond with rainbow trout this year. Usually, from spring through fall, the department stocks the pond with 4,000 catchable rainbow trout.

"Post Falls Park Pond is our most popular community fishing pond," said Andy Dux, regional fishery manager for Idaho Fish and Game.

"It’s unfortunate that we're not going to be able to provide those fish," he said. "It's one of those negative things that happens when people introduce invasive species into our waterways."

He said Fish and Game is supportive of efforts to manage the snails.

Chinese mystery snails, also called trapdoor snails, are popular aquarium creatures that are native to Southeast Asia, Japan and Russia. They can reach more than 2 inches and have thick shells, according to the Ecological Risk Screening Summary on the U.S. Fish and Wildlife Service's website. The snails are also quick to reproduce and live in high densities, as many as 40 per square meter.

"These invasive snails can clog water-intake pipes and may also transmit diseases and parasites to fish and other wildlife," U.S. Fish and Wildlife said in a July 2020 Facebook post. "They compete with native snails for food and adversely affect aquatic food webs."

According to the Smithsonian Environmental Research Center, "unlike most freshwater snails, they give birth to live young. The sudden appearance of baby snails surprised agriculturalists, hence the name mystery snails."

Fair said as much as the city doesn’t want to close the pond, it's better to close it for the summer than to lose it for good.

The big thing is the snails are there, "and now we have to deal with it,” he said.