Lake Merwin

Merwin Reservoir was formed after the completion of Merwin Dam, in 1931 by the Inland Power and Light Company. The reservoir fluctuates depending on the amount of run-off making boat access difficult at times.

Kokanee are the main target, however, Tiger Muskie planted in 1995 are also popular with anglers. This North Fork Lewis River impoundment located near the town of Ariel, on the south side of Highway SR503, is shared by Clark and Cowlitz counties.

All Bull Trout and Dolly Varden must be released.

PacifiCorp operates boat launches at Speelyai Bay and Cresap Bay. There is a fee to launch on weekends. Call 800-547-1501 for updated reservoir levels.

There is very limited shore access.

Two-pole fishing is allowed

Shoreline access: Good - Very limited.

Species you might catch

Lake information

Counties: Cowlitz, Clark
Acreage: 3835.60 ac.
Elevation: 242 ft.
Center: 45.979477, -122.448448
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Catchable fish plants

Release Location: LK MERWIN (COWL)
Stock Date Species Number Released Number of Fish Per Pound Facility
Jul 13, 2022 Rainbow 583 1.33 MERWIN HATCHERY
Jul 13, 2022 Rainbow 583 1.33 MERWIN HATCHERY
Jul 13, 2022 Rainbow 979 0.25 MERWIN HATCHERY
Jul 13, 2022 Rainbow 988 0.25 MERWIN HATCHERY
May 9, 2022 Tiger Muskie 1,600 3 MESEBERG HATCHERY
Jun 8, 2021 Rainbow 1,224 0.28 MERWIN HATCHERY
May 10, 2021 Tiger Muskie 1,600 2 MESEBERG HATCHERY
Apr 19, 2021 Rainbow 1,207 0.28 MERWIN HATCHERY
Apr 19, 2021 Rainbow 3,000 2.5 MERWIN HATCHERY
Jun 22, 2020 Rainbow 1,065 0.25 MERWIN HATCHERY

Fishing prospects calendar

Rainbow trout

Fishing success for Rainbow Trout is generally best in the spring when thousands of fish are stocked statewide, but they can be caught year-round in most waters with a little patience and persistence. Success remains high into June and gradually declines as water temperatures increase and fish move offshore to stay cool. Fish that escaped the spring harvest return to the nearshore areas in the fall as waters cool off. Some waters may also be stocked again in the fall further boosting catch rates.
Chart showing fishing prospects throughout the calendar year


The Kokanee fishery typically lasts from April-October before the adults leave the lake to spawn in tributaries starting in late-October and early-November. Fishing is best in the spring before they move into deeper water to avoid warming water temperatures, but they can be targeted throughout the summer in deeper offshore areas near the thermocline. There may be a slight uptick in some waters in the fall as adults return to shallower water and move near shore towards spawning tributaries.
Chart of fishing prospects throughout the calendar year

Northern pikeminnow

Fishing success for Northern Pikeminnow increases in May and June as water temperatures increase, and generally peaks in late June, although fishing conditions can vary throughout the Columbia River. After a lull during the heat of summer, fishing success peaks again in late September-early October. Northern Pikeminnow congregate in rocky areas with fast currents near dams, islands, stream mouths, points, eddies, rows of pilings, and ledges or bars in the river. Sunrise, sunset, and night are generally the best fishing times. Studies show there are greater concentrations of Northern Pikeminnow in shallow water during low-light conditions.
Chart of fishing prospects throughout the calendar year


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