Midges Drive Lake Health

Midges Drive Lake Health

Any tailwater trout fisherman worth this salt will tell you that midges are the go-to fly pattern -- and the dominant insect species -- in the outlet streams immediately below the dams that hold back larger reservoirs. Especially in the colder months, catching big fish on tiny flies is a seasonal discipline and an eye opening rite of passage for those new to the sport. Lake fishermen are also aware of the overall value of Chironomids (belonging to the enormous order of insects called Diptera), and when the hatch gets frustrating, dropping a tailless size #22 emerger in the film below a dry fly has saved many fishing days.

Recent scientific study is indicating that midges contribute more value to the health and vitality of lakes and tailwater streams than has been previously realized. Researchers from the Leibnitz-Institute for Freshwater Ecology and Inland Fisheries in Berlin, working in conjunction with biologists in the UK, have determined that the activity of burrowing midges and certain classes of annelid worms work to increase oxygenation of lake bottom sediments up to 300% more than had been previously assumed. The process, known as bioirrigation, increases infusion of oxygen and promotes aerobic breakdown by bacteria of the fine organic materials in sediment, providing available nutrients for species throughout associated ecological webs.

Using the bioactive tracer dye Resazurin, the researchers were able to measure the contribution of oxygen that the insects were making to the substrate they were burrowing into. Resazurin is light blue dye that turns a bright fluorescent pink after being converted via cellular metabolic processes in living organisms. Resazurin has been used in previous studies to assess the total insect biomass in stream bottoms -- measuring direct respiration of the organisms -- but in the case of the lake sediment research, the amount of converted resafurin in the treated sediment was used as an extrapolation of available oxygen for the midges to breathe in the first place.

 
Photo by Wikipedia

Lakes, especially deep reservoirs in colder climates, are subject to a seasonal change in biology known as "Turnover". A consequence of thermal stratification, turnover happens twice a year. In the late Fall, surface water (called the Epilimnon) that had been cooled by subfreezing air becomes denser and falls to the bottom of the lake, displacing the warmer water next to the earth at the bottom (the Hypolimnon), which then rises to the surface passing through a mixing zone known as the Thermocline. In the spring, the process repeats, but this time with melted ice cover displacing deep, warmer volumes. In both cases, the sediment at the bottom of the lake gets churned, with the entire water column becoming opaque for a period of days to weeks.


This typically includes the outflow to tailwaters. Increased bioirrigation would undoubtedly make water not only more easily turbid with thermal exchange, but also appear to contribute the nutrient health of the sediment, much as soil vitality is of crucial importance to farmers.


I have fished the famous tailwater section of the San Juan River in New Mexico below Navajo Lake at Christmas time, right after turnover. The Juan typically runs extremely clear all year, but during this trip, the water was pea green with maybe only four inches of visibility. I wasn't happy to discover these conditions after making the 400 mile drive from Denver in midwinter, but I suited up and hit the river anyway.


Much to my surprise, the nymph fishing was red hot, and in this case I'm referring the to color of the top fly of the trip. Bright red midge patterns -- as opposed to the typical chocolate and black color variations favored the rest of the year by Juan enthusiasts -- were being crushed on sight by gangs of voracious Rainbows staged in shallow lies with any slightly improved visibility.

 
Photo by Wikipedia

Along with dark purple chenille worms, (again, a departure from the locally favored pumpkin orange for most other months), the midges had apparently been displaced from their lake bottom dwellings into the water column, and flushing with color from the stress of the experience, were being washed out the spillway of the dam into the mouths of the thousands of trout below.

The majority of major river and stream resources in the US and abroad are now dam controlled. This is a necessary part of modern life, with larger reservoirs providing both flood control and drinking water reserves for huge populations of people. The biological health of water impoundments is thereby a priority for society, and matter of national security. If high concentrations of pesticides in lake sediments from agriculturally impacted stream inflows could affect midge biology -- driving a collapse of lake bottom insect life and potential putrefaction of lake water via stagnant sediments, then this needs to be researched more extensively in the interests of both sportsmen and the public at large.


Get Your Fish On.

Plan your next fishing and boating adventure here.

Recommended for You

American Rivers today released its annual list of America's Most Endangered Rivers, identifying ten rivers facing imminent threats. News

2019 Most Endangered Rivers

Fly Fisherman - April 16, 2019

American Rivers today released its annual list of America's Most Endangered Rivers,...

The Kamikaze Sculpin is easy to tie, versatile, and smartly designed to get the job done. Fly Tying

Tying the Kamikaze Sculpin

Charlie Craven

The Kamikaze Sculpin is easy to tie, versatile, and smartly designed to get the job done.

Here's a look at 8 new fly lines for 2019. Lines

8 New Fly Lines for 2019

Fly-Fisherman

Here's a look at 8 new fly lines for 2019.

See More Recommendations

Popular Videos

 Getting Started In Fly Fishing

Getting Started In Fly Fishing

Getting Started In Fly Fishing

Breaking the Surface

Breaking the Surface

Attack of the Bass continues as Breaking the Surface attacks bass with fly and lure 12:30pm ET Sunday, April 17th.

Bahamas - Bonefish

Bahamas - Bonefish

Conway casts for his personal best bonefish while fishing the Grand Bahama islands.

See more Popular Videos

Trending Stories

As you explore your home water, keep in mind what they are are eating to select the best carp flies! Flies

The 15 Best Carp Flies

Jay Zimmerman - September 27, 2016

As you explore your home water, keep in mind what they are are eating to select the best carp...

Golden riches in Wyoming's high-country heaven of the Wind River Range. United States

Wind River Range Wyoming

Greg Thomas - July 27, 2015

Golden riches in Wyoming's high-country heaven of the Wind River Range.

Read about Colorado's backcountry fly fishing in United States

Indian Peaks Wilderness Area Colorado

Steven B. Schweitzer - May 03, 2016

Read about Colorado's backcountry fly fishing in " Indian Peaks Wilderness Area Colorado."

See More Stories

More Industry

It began with love of a river that he fished as a boy with his father, and a passion for the sport that still endures today. Industry

Abe's Fly Shop Turns 60

Jay Walden - February 22, 2019

It began with love of a river that he fished as a boy with his father, and a passion for the...

The 4th Annual Clean the Dream event will be Aug. 10, 2019 from 8 A.M. to 2 P.M. Orange juice, donuts, and trash bags will be provided in the morning, and there will be a BBQ at 2 PM Industry

Clean the Dream

Jonathan Wright - June 24, 2019

The 4th Annual Clean the Dream event will be Aug. 10, 2019 from 8 A.M. to 2 P.M. Orange juice,...

The U.S. National Fly Fishing Championships are slated to be held May 30th through June 2nd, and this year's host city will be Bend, Oregon. Industry

U.S. National Fly Fishing Championships

Jonathan Wright - May 09, 2018

The U.S. National Fly Fishing Championships are slated to be held May 30th through June 2nd,...

See More Industry

GET THE MAGAZINE Subscribe & Save

Temporary Price Reduction.

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE

GET THE NEWSLETTER Join the List and Never Miss a Thing.

×