Stewart Lake is an important nursery habitat for endangered razorback sucker. This project is intended to complement previous mechanical treatments and prescribed fire. The loss of open water habitat due to encroachment of cattails limits production and survival of juvenile razorback sucker in Stewart Lake. In 2019, Open water was limited to 4.6 acres of dredged channels with in Stewart Lake WMA.

This project is intended to ensure mortality of cattails and increase the area of open water habitat within the wetland. Increased open water will increase production of endangered razorback sucker and bonytail and improve habitat for waterfowl.

If cattails continue to encroach, open water habitat may be completely lost and juvenile razorback sucker will be unable to survive in Stewart Lake. Stewart Lake is the only wetland in the upper Colorado River Basin where razorback sucker have consistently survived past the larval stage and is thus one of the most important habitats to the survival of this species.

Bureau of Reclamation Selenium Remediation Record of Decision: ~ The Bureau of Reclamation EIS ROD requires selenium concentrations in water and bottom sediments at Stewart Lake to be reduced to acceptable levels. In order to reach those goals, a drain/dry cycle is required to allow selenium to oxidize during dry periods greater than 180 days. Following drying, a flush of water coinciding with high river flows will uptake selenium and move it out of the Stewart Lake system. Dense cattail vegetation inhibits both drying and flushing. This project will address these factors. Upper Colorado River Recovery Project--Razorback sucker larval trigger study plan: ~ The larval trigger study plan involves timing releases from Flaming Gorge Reservoir with razorback sucker larval presence to entrain them into flooded wetlands. A major component of the larval trigger study is sampling and monitoring. Dense cattail vegetation limits the ability to sample the project area. Utah Wildlife Action Plan: ~ The Wildlife Action Plan identifies a number of the species and habitat identified in this project as priorities. The project addresses some of the threats and risks for these species and habitats as well.

This will reduce fuel loads of highly flammable cattail stalks. The increase or open water will provide a fire break in the event of ignition. Stewart Lake is bordered by residential dwelling that would be at risk in the event of a fire.

Reducing cattail stands should prevent water loss from transpiration and thus increase water quantity. Reducing the production of stalks could reduce the biological oxygen demand in subsequent years and deeper water maintains cooler temperatures, both of which will provide better water quality for fishes and aquatic organisms.

Project is entirely on UDWR land, no NEPA required. No ground distubance; no ACRH clearance required.

Arial application of herbicide in July or August 2020.

NER aquatics and habitat staff will monitor for effectiveness and additional treatment needs.

Consultation with US Fish and Wildlife Service and US Bureau of Reclamation

If large scale mortality of cattails can be achieved, smaller scale herbicide applications may be used to maintain open water and slow encroachment. Prescribed fire may be used to reduce fuels around the perimeter of open water and further slow encroachment into created open water habitat.

This will preserve and promote populations of endangered fishes primarily razorback sucker and bonytail. Increased open water may also benefit waterfowl hunting in the future.

09/01/2020

10/30/2020

2021

Spraying occurred August 2020 by Hammond Helicopter with Rodeo at a rate of 3 quarts per acre. 200 acres +/- in the Stewart Lake Waterfowl Management Area were treated, comprising the majority of the wetland habitat that is inundated during high flows of the Green River.

Open water habitat has been nearly eliminated by encroaching cattail and bulrush stands in the Stewart Lake wetland since drain and dry cycles were implemented to reduce selenium concentrations in bottom sediments. Open water habitat is desirable because it is used as a nursery for endangered razorback sucker and, to a smaller extent, bonytail. Cattail and bulrush stands may also impede drying and flushing of sediments for selenium mitigation and pose a fire hazard. Cattail and bulrush stands in the treated area have experienced near complete mortality during the growing season following treatment.

Cattail management at Stewart Lake will continue. Smaller scale herbicide treatments may be undertaken as cattails begin to return to the periphery of the wetland. Prescribed burns and drying during drought years may also be utilized.