The Gunpowder Falls Tailwater: Assessing One of Maryland’s Coldwater Trout Fisheries

Maryland Department of Natural Resources staff assist with netting trout during a survey of the Gunpowder River. Photo by AJ Metcalf/Maryland DNR.

On a brisk September morning, fisheries biologists with the help of an electrofishing pontoon barge and a 12-person net crew waded central Maryland’s most popular self-sustaining brown trout fishery searching for what lies beneath the surface.

Between the Prettyboy Reservoir and the Loch Raven Reservoir is a 17-mile stretch of fertile trout habitat, where wild brown trout have flourished since the late 1980s due to one of the Maryland Department of Natural Resources’ greatest success stories.

Prior to 1986, the gates of the Prettyboy Dam would open and close as seen fit by the City of Baltimore. The reservoir’s drainage leads into the Gunpowder Falls, which moves toward the Loch Raven Reservoir, funnels into the Big Gunpowder Falls, widens into the Gunpowder River, and empties into the Upper Chesapeake Bay. When the gates of the Prettyboy Dam were closed, the upper span of the river effectively dried up.

Fisheries biologists measure and weigh the trout to estimate a population density. Photo by Hunter Dortenzo/Maryland DNR.

In 1986, DNR officials along with the Maryland chapter of Trout Unlimited worked with dam officials to negotiate a minimum flow, keeping gates open at all times to provide constant cold water release. The cold water comes from the depths of the Prettyboy Reservoir, typically under 55 degrees year-round, and ideal for wild trout populations. When the agreement was made for the dam to release water year-round, department officials tested the area’s capability to sustain a brown trout fishery.

“Within four years, we had a thriving brown trout fishery that has really expanded and taken off beyond our wildest dreams,” said Mark Staley, DNR’s Central Region Fisheries Manager. “The management has changed – in the past we used this as a put-and-take stream. Once we applied catch-and-release management, we found that brown trout were reproducing and had great numbers. It’s been a big, big success.”

Today, the area is renowned as one of the nation’s best trout streams and for its proximity to the populous Baltimore area.

Crews deploy anodes from the electrofishing pontoon barge, which expel electrical current to briefly stun the fish. Photo by Hunter Dortenzo/Maryland DNR.

Being a tailwater–meaning water located downstream of a hydraulic structure, in this case a dam–this fishery shares features with other productive trout streams in Maryland, particularly in the western region of the state. The typically colder waters of the Savage, Youghiogheny, and Casselman rivers are other go-to destinations for anglers to pursue brook trout, wild brown trout and hatchery-raised rainbow trout.

“The Gunpowder has a very dense trout population,” Staley said. “It compares very well to Western Maryland streams–maybe even more dense, as far as numbers of fish. We have a lot of fish, most in that 8-9 inch range. But we have seen some fish 24 to 30 inches and up in the very deepest pools.”

The geographical features of Harford and northern Baltimore counties contribute to the success of the Gunpowder’s trout population. Its proximity to metropolitan areas is key for public access and has several natural features working in its favor. Grassy and shallow areas on the edges of the stream are important habitats for the younger, smaller trout, where staying away from larger fish may be the difference between life and death. Brown trout are an extremely predatory species which are known to eat small fish–including their own young–in addition to the standard diet of aquatic insects. In the Gunpowder those insects typically range from mayflies to caddis to stoneflies.

Fisheries biologists place wild brown trout on a measuring board as part of the survey, in which the fish are released after. Photo by Hunter Dortenzo/Maryland DNR.

The river also has features such as riffles–shallow, fast-moving, and oxygen-rich waters–where the trout position themselves downstream as they feed on the insects that lurk above. Bigger fish gravitate toward deeper, colder pools, guarded by the Gunpowder area’s scenic rock outcroppings and boulders. The combination of the riffles, runs, and shallow and deep pools work together to create a well-balanced population of insects and trout in the stream.

Surveyed annually by DNR scientists since 1988, the Gunpowder has stayed remarkably consistent in its trout population numbers. The study measures the young-of-year trout densities, assesses the standing crop of adult brown trout, and monitors the length and weight of the trout collected.

Scientists use the electrofisher to briefly “zap” the fish with a high-voltage, low amperage current, then the netting crew retrieves the trout, and groups them in live-wells before the fish are analyzed, measured, and safely released. This year’s survey collected 277 wild brown trout in addition to several other species who call the Gunpowder home. Blue Ridge sculpin, northern hog suckers, white suckers, pumpkinseed sunfish, and American eel were found in the quarter-mile stretch of the stream that was surveyed.

Prior year surveys have identified citation-sized brown trout, holdover rainbow trout, native Maryland brook trout, and the ultra-rare brook/brown hybrid “tiger” trout. While 2024 survey results will take some time to formulate, early assessment indicates no reason for concern.

“We saw good numbers of fish,” Staley said. “From seeing multiple year classes, different size classes and good reproduction, there is every indication that the population is healthy and providing good fishing.”