Lake Profile: Merwin Reservoir

[Don Wittenberger]

Merwin Lake is a hydropower reservoir located about 35 air miles northwest of Portland on the North Fork of the Lewis River, which flows 93 miles from Mt. Adams to the Columbia River. The lower reach of this river is an important migratory salmon and steelhead stream and endangered bull trout inhabit portions of the watershed, including Yale and Merwin lakes. (The bull trout can’t reproduce in Merwin Lake, but some come down fromYale Lake above.)

Merwin Lake was created by the construction of Merwin Dam between 1929 and 1931 (additional generating units were added in 1949 and 1958). The dam, 19 miles upstream from the Columbia River, is 313 feet high and 1,300 feet long. It is owned and operated by Pacific Power, and generates power for about 66,500 homes. There are two safety barriers above the dam, and watercraft are not allowed in this restricted zone.

The 4,090-acre reservoir is 14.5 miles long and averages about ¾ mile wide, runs in a generally east-west direction, and has more than 25 miles of shoreline with bays, coves, and stream inlets. At full pool, the surface elevation is 239.6 feet above sea level, and its maximum depth is 190 feet in the vicinity of the dam. Because it occupies a former river canyon, the reservoir is narrow and deep, with quickly dropping shorelines, and has no midlake structure. It does, however, have several large flats, and these can be navigation hazards because of shallow water or submerged stumps. The old river channel meanders on the bottom, snaking from one side of the reservoir to the other, and where it brushes shore the bottom drops abruptly to a depth of 60 to 100 feet. Although the lake as a whole is not rocky, it does have some rock walls, boulders, and underwater rock ledges. As a reservoir with water flowing through it, the lake has a current (usually slight), and does not develop a thermocline. The water temperature is more or less uniform temperature to a depth of at least 30 feet; this lake does not have Mayfield Lake’s sharp temperature gradient, and tiger muskies often are found deeper here than in Mayfield Lake. The surface water temperature can reach the 70s in summer, and cools to 62 degrees in mid-October, by which time the tiger muskies are no longer fishable.

Nearly all of the shoreline is undeveloped, and will remain so because it is owned by the power company and managed for wildlife habitat pursuant to the operating license and agreements with government and tribal entities. In addition, there are numerous legally protected archaeological sites (of ancient Indian villages) in the immediate vicinity of the reservoir, therefore no boat camping is permitted anywhere on the shoreline. Much of the shorelineis bordered by forested hillsides, and many trees fall into the lake. There is a vast array of submerged stumps and logs along the shorelines, and much of the bottom over the littoral zone where tiger muskies are found is a jumble of rotting stumps and jackstrawed logs. At times, the surface is littered with floating logs and wood debris, which is a navigation hazard when present. The lake has a 40 mph boat speed limit, and is regularly patrolled by the Lewis County Sheriff’s Department marine patrol.

The lake and its environs sport some colorful lore. Federal authorities believed airplane hijacker D. B. Cooper bailed out over the lake, and the lake bottom in the vicinity of the dam was searched for his body. In addition, sasquatches are alleged to inhabit the surrounding hills and hollows.

Merwin Lake received its first plant of tiger muskies in 1995, and fish exceeding 30 lbs. are known to exist here. As in most Washington lakes, the fishery is dynamic; that is, constantly changing. Even if I was willing to disclose where my “spots” are, it wouldn’t do you much good, because this changes every year. In 2004 and 2005, I caught most of my fish in shoreline cover, but they disappeared from the shorelines in 2006 and I caught nearly all of mine by fishing the dropoffs. The number of fish my party saw in 2006 plummeted from previous years, raising a question as to whether the tiger muskies have eaten out much of their food supply and suffered a population crash. They may have reduced the squawfish by as much as 90%, and there is little evidence they feed on the lake’s abundant kokanee. It also stands to reason that as tiger muskies grow larger, they need more food, and the lake’s food supply can support fewer of them. If the population is declining in tandem with a shrinking food supply, then we should find dead muskies, and in fact we were indeed finding numbers of dead muskies on the bottom in the 2006 season, which would seem to confirm this hypothesis. However, I’m not a biologist and I may be wrong on all of these counts. Based on my own fishing experience, this is not as good a lake as it was a couple years ago, and the tiger musky population does appear to be thinning out. Harvest may also be a factor, as Merwin Lake’s tiger muskies are now receiving considerably more fishing pressure.

The key strategic consideration in fishing this lake is that food supply, not habitat, is the population-limiting factor. Consequently, there is an awful lot of great-looking habitat and shoreline cover that doesn’t hold fish, and efficient search tactics are more essential here than in any of our other tiger muskie lakes. This lake is too large to fish in one day, even if you move quickly and fish efficiently, so you should break it down into areas, and fish it area-by-area.

I generally use a mix of heavy-bodied bucktails and crankbaits, and sometimes add weighted leaders or bell sinkers to get them to run deeper. In the past, the water usually have been very clear with the bottom visible to 25 feet, and throughout the 2006 fall season I was successful by fishing at a depth of 15 to 20 feet. A tiger muskie resting 30 feet down could see the lure, and they would come up to get it. Nearly all of these “dropoff fish” were well below my lure, which means they were at least 25 feet down. But over the 2006-2007 winter, mud washed into the lake from a housing development overlooking Cresap Bay, and if the water stays murky into the summer, we may have a shallow water fishery again in the 2007 season. Otherwise, I will continue to work the dropoffs, and this consists of endless hours of zombie casting that isn’t much fun. I usually use a weighted in-line bucktail for this work.

As at Mayfield Lake, the best time to fish for Merwin’s tiger muskies is from mid-June into early October, and the fish here probably are feeding exclusively (or nearly so) on squawfish.

One factor that helps to limit fishing pressure and protect Merwin’s muskie population is limited accommodations near the lake and limited public boat access. Most of the anglers who come here are kokanee trollers. A handful of savvy bass anglers clean up here, because this lake has a limited population of good-sized largemouth bass that are virtually unfished. An angler told me of catching smallmouths here; if smallies get established in the lake, that could lead to increased food supply and more tiger muskies. If you want to fish for bass, look for them in rocky areas.

There are two fee boat launches, both owned by Pacific Power and operated by a contractor hired by the power company to run its recreation facilities. These are located at Speelyai Bay and Cresap Bay. The only motel near the lake is Lone Fir Motel in Cougar, 5 miles away, and you’ll need reservations during the fall hunting season. Meals are available at Jack’s Restaurant, located about a mile east of the turnoff to Speelyai Bay, and at a café in Cougar 5 miles farther east. Both are reasonably priced and the food is decent; Jack’s has become a morning gathering place for muskie fishermen.

The only campground on the lake is at Cresap Bay, which offers overnight docking of boats for an additional fee. B