Diving for weeds

Clogged boat motors. Tangled fishing lines. Dense patches of weeds that can make swimming unsavory. Aquatic weeds can mess up all kinds of recreation on a lake or river.

Non-native aquatic invasive species can also crowd out native plants and alter the ecosystem of a body of water. But removing them is a real challenge.

Avista implements three aquatic weed management programs related to our hydroelectric facilities on the Spokane River. On Coeur d’Alene Lake, Lake Spokane and the Nine Mile reservoir, we collaborate with public agencies, tribes and other local stakeholders to eliminate or reduce the impact of aquatic weeds.

One of the invasive aquatic weeds that Avista targets for control is Flowering Rush. Its presence is increasing annually, and it is known to be problematic in other waterways in North America. It entered the Spokane River from the Hangman Creek drainage and it is now present in Nine Mile Reservoir and Lake Spokane.

One strategy to combat Flowering Rush involves divers pulling the weeds out by hand. Flowering Rush is a hardy plant with large rhizomes that make it difficult to eradicate. Divers carefully dig up the roots from the river bottom and then feed the weeds into a vacuum that deposits them in a boat.

This year, Avista contracted with divers who spent 11 days pulling Flowering Rush from Lake Spokane. They filled 117 totes, each with a capacity of 17.5 gallons, removing almost three tons of wet plants.

“We’re hoping to stay ahead of this problem,” said Rob Stephens, Avista restoration biologist.

At the Third Street Boat Launch in Coeur d’Alene Lake, we employed divers to remove Curly-Leaf Pondweed, which first showed up in the lake in 2018. Divers removed 368 gallons of the non-native weed in 30 days this year. Additionally, two herbicide treatments were conducted in 2019 to remove the invasive weeds. Curly-Leaf Pondweed was most likely introduced there by a trailer and boat with a fragment of the plant that came from another lake where it already occurred. Previously, Coeur d’Alene Lake only had one invasive species, Eurasian watermilfoil.

“Any time you’re moving a boat from one body of water to another, there’s potential to carry out aquatic weeds from one lake and infest another. The weeds can have huge impacts on ecosystem health and recreation,” said Rob. “That’s why it’s so important to thoroughly inspect your boat prior to driving away from a boat ramp. Follow the guidelines to clean, drain and dry your boat, and you’ll help prevent the spread of invasive species.”

“We are fortunate to have the abundant lakes and rivers we do in this region. It also presents a challenge to manage these water bodies with finite resources. It's through collaboration with Avista, the Coeur d'Alene Tribe, Idaho Department of Environmental Quality, and the Idaho State Department of Agriculture that we are able to keep an eye out for new infestations,” said Jamie Brunner, Lake Management Plan Supervisor for Idaho Department of Environmental Quality. “It's important to be able to detect new invasive species early and take action as quickly as possible. Thanks to Avista's role in managing aquatic weeds, Curly-Leaf Pondweed in Coeur d'Alene Lake has received early action to try and keep this weed from spreading.” Additional thanks go to the Hagadone Marine Group who has contributed to the curly-leaf pondweed removal effort.

Homeowners can also reduce weeds from their shorelines by building a bottom barrier. Learn how.

Build a bottom barrier


  1. Rivers