Merrill Lake


I’ve actually had the pleasure of speaking at your club in the past and would love to again. I supply the goody bags for the kids in your fly fishing club!!

I will reach out to Officer Chamberlain about Merrill. I wish I could be there tomorrow but have other commitments.

I need to find a way to get the schedules for these groups outings. I work with Riverjunky on the river issues down here in Region 5.
Hello Stace – thanks for joining this forum, I believe that you have posted over on ifish before on this topic several years past. First, like others on this forum has already mentioned, kudos to you for reaching out and proactively asking for feedback on a public forum like this. Social Media should be a good tool for other Biologist to collect input from users. Spread the word to your colleagues.

I am from Portland, but I do buy an annual out of state license to fish Merrill and other lakes up in Washington. I have fished Merrill for the past 9 or 10 years and normally hit about two or three times per year, usually once in the Spring, then during the Summer to try to hit the Hex Hatch, and then in the Autumn to try to target the Browns.

Personally, I haven’t seen much of a change in Merrill Lake the time that I have fished it over the past 10 years. For me, it has been catching a lot of THIN Cutts in the 9-11 inch range with a couple pushing up to 13 inches. I don’t recall ever catching Cutt over that size. I would say that most of the Cutts that I do catch seem to have the Parasites that you previously mentioned on their fins. The Cutts don’t have much fight to them. I am not sure if that is due to the Parasites or just the nature of the Cutts. I have always been unimpressed by the Cutts in Merrill – and they make up the majority of my catchs.

I have caught a handful of smaller Rainbows as well in the same size range. I recall that they too had the Parasites on the fins as well, but seemed to have more fight to them than the Cutts. I also hit Merrill once after WDWF stocked it with the Triploids a few years back. I caught a couple of that were in the 18 inch range and seemed fairly healthy, but I believe it was just a few weeks after they were stocked. They put up a decent fight, but nothing like other Triploids in other Washington Lakes. I don’t think the Triploids did well, as I had friends fished Merrill later that summer and into the Fall that caught a few of the Triploids and they were heavily infected by the parasites and he mentioned that they didn’t put up much of a fight. I don’t recall catching or hearing anyone else catching the Triploids the following year.

The Brown Trout in Merrill is what keeps me coming back. I have probably caught less than five Browns in all of my trips up to Merrill – but the few that I do catch are seem plumb and seem healthy and fight well. I have never seen the Parasites on any of the Browns that I have caught. They are also bigger than the Cutts and the non-Triploid Rainbows. I have seen some big Browns rise or swim by and heard of multiple fishermen catching nice sized Brown Trout. They aren’t easy to catch, but I enjoy the challenge of trying to catch a large Merrill Lake Brown Trout.

If it wasn’t for the Brown Trout – I am not sure if I would fish Merrill. Maybe to hit a Hex Hatch or two since that can be fun just to witness the Hatch itself and have the opportunity to catch some sick Cutthroat/Rainbows on a big dry fly is fun.

I am no Biologist by any means – but with the Diphyllobothrium issues in Merrill Lake, what options do you really have? What I have heard is that the Diphyllobothrium issues impacts the Rainbows and the Cutts and doesn’t really bother the Brown Trout.

My assumptions has been Diphyllobothrium issues is what keeps the size down on both the Cutts and the Rainbows – the parasite will eventually kill the fish and that is why there is not many Cutts above the 11 inch range. Is this true?

And is there enough feed in the Lake for the Cutts and the Rainbows? Besides the Hex and Alder Fly Hatch and I do see a few Damsels and Dragon Flies around, but Merrill Lake doesn’t seem like a bug factory to me, but that is pretty typical for most Western Washington & Oregon Lakes. My assumption is that the Browns get big by feeding on the Cutts, and other fish, plus the Hex as well.

Are the Cutts and Browns stocked – or are they self-sustaining and reproduce naturally? My assumption has always been they are not stocked and reproduce naturally. How about the smaller Rainbows that I periodically catch as well, are they stocked as well?

Since you are asking our opinion about stocking the lake with the 1500 Catchable Rainbow Trout – my answer is what is the point if they are going to be impacted by the Diphyllobothrium issues or die off before they can grow to the Trophy size range (16+ inches)? Seems like you have your hands tied on this one – unless you make it an exclusive Brown Trout Fishery and stock more Browns in there – but with out the Cutt’s and Bows – not sure that they would grow as large as they do today. Plus since they are Browns are harder catch- the general public would probably continue to be concerned. The general public seems to be more concerned about quantity vs quality of fish. Not me, if I could go up and spend the day to catch a half of dozen Trophy Brown Trout – that would be just fine by me. But until the Diphyllobothrium issues can be solved (unlikely) or goes away – I don’t think there is much you can do.

Once last item – as other have mentioned as well – I do see a lot of the rules being broken up there, plenty of folks that are not fly-fishing and I have seen more than my fair share of Powerbait containers and styrofoam worm containers.

Please feel free to reach out to me if you have any questions or need any clarifications. Just private message me through this web site and I will be happy to assist.



Active Member
Hi Stace.... good to see you up on this Forum! I'm a member of CSF (Clark-Skamania Flyfishers) and we have a Merrill Lake clean up tomorrow (Saturday 31st) with the DNR, and hope to see you (and anyone else that would care to join us at 9am) up there. The hope is they (DNR) will leave the gate open then, for the rest of the season. My biggest concern with Merrill has been poaching, and people fishing with gear... it's rare that I don't see someone with a spinner. I was the conservation chair at CSF, and we supplemented the triploids that WDFW put in the lake. The word got out, the fish were gone in less than two years...and it's been in a steady decline since.
I see you are a biologist... we need you to come to one of our CSF meeting for a show and tell!
If signs were posted about the Diphyllobothrium issue with the fish, how likely would the poaching problem take care of itself? Just make sure the signs explain how long those things can get. And pictures. Lots of pictures.


Active Member
Welcome to the forum Stacie and thank you for the opportunity to comment on the future of Merrill Lake.

For more than 20 years I’ve fished Merrill year-round, hiking in at the north end and dragging my pontoon in from the locked gate during the winter when road conditions allowed. Never have I been disappointed even when the fishing was less than stellar due to conditions or timing but never because of a lack of fish.

This past October a friend and I had an extraordinary day at one point a fish per cast on dry fly’s. We then switched to casting streamers and continued the catch rate, even casting to and hooking some spawning browns. The cutthroats were larger and healthier than I’ve seen in a while with little or no parasites evident which are normally prevalent at that time of year. Fish averaged 12”-14” with some near 15”. A reduction in fish numbers is not something that we have noticed. I would suggest that reports of low success rates have nothing to do with the fishery but rather the individual and timing.

Some points I consider to be important:

-Merrill is the only fly fishing only lake (to my knowledge) that is accessible to fishers unable to make the long hikes into other naturally reproducing cutthroat fishing waters.

-It is a natural ecosystem. How many do we have left?

-How many fly only lakes do we have in this region? Statewide?

-How many planted lakes do we have already, do we need another?

-Why plant hatchery raised fish without an understanding of exactly where the fishery stands and if in decline the reasons.

- Why is it important to curtail hatchery plants to protect natural fish runs (Cowlitz river sea runs), but not in this case?

-If we must plant something I would recommend Hexigina Limbata nymphs, they seem to be in decline.


Active Member
An interesting discussion and sounds like there are two parasites (both of which are pretty common in western Washington lakes) that are infecting the trout. Since I have never fished Merrill or even seen the fish so be out to lunch with the following-

The external parasites at the base of the fins are likely one of the parasitic copepods that are common in western Washington. They typically are the size of a grain of rice and as mention typically found at the base of the fins, and in the mouth and gills. Except in extreme infestations the trout are not harmed and survival does not seem to be affected.

The Diphyllobothrium (trout tapeworm?) on the hand can be a real problem resulting in reduced survivals; especially for rainbow trout. As with many of the parasites the Diphyllobotrhrium has a complex live history with the trout being infected by eating infected zooplankton. Once in the gut of the trout the parasite breaks out of the zooplankton and migrates through the fish's body causing damage and in many cases significant mortalities. That mortality typically occurs in the mid/lat summer following the trout eating the zooplankton during the spring/early summer "blooms". The rainbows tend to consume those zooplankton more frequently than some of the other trout. As the rainbows grow their gill raker spacing increases and they become less efficient in capturing and consuming those zooplankton; that is once the fish reach about 15 inches the zooplankton become a less important food item. Because the gill structure of the cutthroat and browns are more coarse (better designed to be a predator?) they tend to be less vulnerable with those zooplankton being an important part of their diet at a smaller size than the rainbows. If there are alternative food sources (less reliant on zooplankton) for the smaller cutts and browns some will avoid the parasite. On some lakes managers have had some success in increasing survival of planted fish by releasing them at a larger size and/or in the fall.

It has been observed that if the goal is produce larger carry-over rainbows in at least in many western Washington lakes the normal diploid tend to preform better than triploids.

BTW -The Diphyllobothrium (have forgotten the species) in these lakes is a different tape worm than the one that infects humans (D. latum?) with a different group of final hosts (birds versus mammals).



Active Member
The third parasite is a poacher.... Back in the summer of 2009, CSF got Rick Hafele and Dave Hughes (Western Mayfly Hatches) to come up to Merrill and help us with a bug (bio-mass) survey. I've found a few pictures from that expedition, and have a DVD and written report that Rick produced around here somewhere... I'll post it when/if I find it. I know a copy was given to John Weinheimer.. the district 5 biologist back when we did it. What we found (in that very limited snapshot in July) was .. not a lot. Basically there was the Hexagenia nymph, (of course) Alderfly larvae, an assortment of midges, (Dave knew what kind) and crayfish... a fairly hungry lake! I've heard there is a good callibaetis hatch at the south end, but I've never seen it. We need to do more surveys, and it might be fun to have Stacie lead a group... maybe in the Fall?


Active Member
"They will be monitored by way of on-site creel and I’m hoping anglers will participate in a Volunteer Angler Diary Program I am creating. "

Any progress on this Stacie?


Active Member
"They will be monitored by way of on-site creel and I’m hoping anglers will participate in a Volunteer Angler Diary Program I am creating. "

Any progress on this Stacie?
I got a note from Stacie a few days ago, and she said the fish will be released early next month, and the log should be set up by then.

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