Invasive New Zealand Mud Snails Found In Private Montana Hatchery, Now Under Quarantine Until Eradicated

Last month Montana Fish, Wildlife and Parks discovered an established population of New Zealand mud snails at a private commercial fish hatchery south of Hamilton.

This discovery marks the first time New Zealand mud snails have been found west of the Continental Divide in Montana, but populations are known to exist in Idaho, Washington, Oregon and California.

These snails are an aquatic invasive species, which once established in a natural system can have localized impact to aquatic ecosystems. New Zealand mud snails do well in cold water environments and are present in several water systems east of the Continental Divide including the Madison, Missouri and Yellowstone rivers.

The Bitterroot hatchery is now under quarantine by FWP, which will last until the New Zealand mud snails are eradicated from the facility.

The snails likely arrived at the Bitterroot hatchery from a fish hatchery in South Dakota, which was thought to be free of AIS until notice this summer that New Zealand mud snails had been discovered there. The Bitterroot hatchery imports trout from the South Dakota hatchery annually.

In Montana, private fish hatcheries are used to stock private ponds with fish. The hatcheries are permitted by FWP and inspected for fish disease and AIS annually. FWP hatcheries only stock private ponds that provide access for public fishing.

The Bitterroot hatchery receives annual inspections from FWP for fish disease and AIS, and New Zealand mud snails were discovered this year.

The Bitterroot hatchery drains into an irrigation canal, not the Bitterroot River. FWP staff have surveyed areas of the Bitterroot River and Skalkaho Creek, both of which are near the hatchery, but have not found any invasive snails.

The Bitterroot hatchery has stocked around 100 ponds in western Montana in the past two years and FWP is in the process of reaching out to those pond owners. FWP has a New Zealand mud snail fact sheet available on

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