Why is the Farmington River so warm? Or: when tailwaters don’t work

I’ve been getting a lot of questions about Farmington River water temps. The basic outline is, “I thought the Farmington is a tailwater. Why is the river so warm?” The answer is pretty simple.

In case you don’t know, a tailwater is a river with a dam release. The flow of the Farmington River West Branch is controlled by water that comes out of gates from the base of a reservoir dam (Colebrook Reservoir and Hogback Dam). If you’ve ever gone swimming in a pond or lake, you know that the water is warmer near the surface and colder near the bottom. This is called thermal stratification. In a larger reservoir, you have three different thermal layers: the epilimnion (the warmer upper layer; the metalimnion (or thermocline, the middle layer); and the hypolimnion, the coldest bottom layer. But I said this was simple, and there I go throwing all kinds of hifalutin hydro-science terms at you.

Ideally, there’s a happy medium of bottom release flows on a tailwater: cold water is never released in amounts that cannot be quickly replenished. But there are two situations that screw everything up.

The first is severe drought. Water that flows into the Colebrook Reservoir is reduced to a warm trickle. The volume of the reservoir shrinks from evaporation. The temperature of the water rises, especially if it’s hot, which decreases thermal stratification. As a result, what comes out of the bottom of the dam is warmer than ideal. (By agreement with the CT DEEP, the MDC must maintain a minimum release of 50cfs.) Because the flow is so low, water downstream warms quickly, trout get stressed, and it’s a bad scene all around. (This was the case in 2016. It was so bad that the DEEP took the unprecedented step of declaring thermal refuges on the Farmington.)

But that’s not what happened this year. This year, we had too much water. All that rainfall in July meant that the MDC needed to bleed water, and lots of it — so much, in fact, that it wiped out any meaningful thermal stratification in the reservoir. They’re still running such a high volume of water that there’s no chance for the stratification to re-establish — at least not in the heat of August. So that’s why at noon today the water was coming out of the dam at a very trout-unfriendly 69 degrees.

Eventually, it will get better. But right now, the best thing you can do for Farmington River trout is play the waiting game.

Taken this winter when the water was very, very, cold. Hang in there, buddy!

Farmington River Report 5/4/21: North, Miss Teschmacher

I guided Andrew and Brett yesterday and they wanted to focus on wet flies. Monday’s rain was more than I expected, and I didn’t like the height or the color of the Permanent TMA. So we headed north to the friendly confines of WBATSR (West Branch Above The Still River. I just made that up.) This was a good call as the water was running a crystal clear and very wadeable 200cfs. I really liked that height, and I thought there were dozens, if not hundreds of pockets and seams and slots and riffles that would hold trout. Sadly, the trout didn’t get the memo, and we had a very slow day. (We didn’t see any angler other than our group hook and land a fish.) It was the kind of day where I find the next great piece of water, and think to myself, “this is going to be it,” and then nothing happens. These episodes make me throw up my hands and say, “I quit.” Of course, I don’t really mean it, and of course we don’t quit, but I get frustrated just like everyone else.

Andrew had fished with me before, and on that day we had far more active fish than today. Brett is a relative newcomer to fly fishing, and once we smoothed out a few wrinkles he was swinging like a pro. I alternated between both anglers, and we worked downstream, covering several hundred yards of water. Bug activity was very light, with two confirmed Hendricksons and a handful of BWOs, but that was it. As you can imagine, angler traffic was heavy, especially with that section of river the only clear water game in town. With today’s rain and increased flows, I would guess that streamers and nymphing will be, by far, the most productive methods for a few days.

Andrew doing battle with a chunky rainbow. He scored two trout, both on the bead head soft hackle I had tied on in the point position. In my experience, wet fly can be challenging in high flows, so I’d wait for the water to get down to 500 or less before swinging. Great job, Brett and Andrew, for persevering though some tough fishing conditions!

Is it OK to fish the Farmington in low summer flows?

I received a great question today: “How about a straight answer about fishing the river at the level it is at right now. I was told I’m crazy for staying away – my thought is it’s not good for the fish or the fisherman. Be honest please.” I’m assuming the question is about the Farmington.

Those of you who know me know I have nothing to sell you but the truth. So here we go.

The simple answer is: most of the time, yes. The Farmington is, after all, a tailwater. If you’re unsure what that means, its flow is generated by a bottom dam release, in this case Hogback Reservoir. In an average year, the reservoir will have a good amount of water in it, such that the bottom strata will be much cooler than the surface. I can tell you from experience that I’ve shivered for hours in the river on a 90 degree day in July. That water is plenty cold.

Fog is what happens when frosty water meets warm, humid air. This shot is from mid-summer.

Morning Fog

What happens in a drought year? In the most extreme years, it can get ugly. Go back to our most recent severe drought year, 2016. The water release was in the paltry double digits, and because there was so little water in the reservoir, what was coming out of the chute was in the mid 60s — not good. Take that water, bake it over several miles, and we had fish kills. The DEEP even declared thermal refuges, unprecedented for the Farmington River. I advised people to not fish.

So what about right now? The release is 118cfs, not great, but it’s coming out cold (the Still is adding 12cfs for a total of 130) as we had plenty of water this spring. Where you fish matters. The run from Hogback to Riverton right is plenty healthy for fish. Naturally, it will warm as it travels downstream. The water may be stressful to trout by the time it gets to Unionville. But every day is different — today it’s cloudy and in the upper 70s, not exactly a river-under-a-heat lamp. If it were sunny and blast-furnace hot, you’d have a different dynamic.

When you fish matters, too. From dawn through when the sun tops the trees is the coolest the river will be on any given summer day.

In conclusion: Use the stoutest tippet you can to get those fish in fast. Don’t take them out of the water. Fish when and where the water is coolest. Use common sense, and you’ll fish with a clear conscience.

 

“We can’t catch a break.”

This just in from Farmington River Anglers Association president Drew Butler: “Sorry guys, but I just received word they are bumping the release from the dam back up to 500 from the current 330 cfs level. Combined with the slowly dropping Still River the total flows through the upper TMA will be back over 800 again. We can’t catch a break lately. I was kayaking on Hogsback Reservoir on Sat and you would not believe the amount of water coming directly into the reservoir from the surrounding hills.”

(This is where we join in a rather large collective sigh.)