Hot Summer Conditions and Stillwater Trout

by Brian Chan

The arrival of our normally hot summer weather brings about many changes to the local fishing lakes and fish behavior. The most commonly asked questions this time of year are:

1. Where and what are the trout feeding on during hot weather? and,
2. Why do fish in some lakes taste muddy?

To answer these questions, one must understand the changes that are occurring within the lake itself. The heat from the sun has now warmed the shallow areas of the lake to the point where the majority of insect hatches such as midges, mayflies, caddisflies, damselflies and dragonflies have occurred. The upper layers of water are now too warm for trout to live comfortably. They will seek the cooler depths where both temperature and oxygen levels are ideal. Thus the diet of many trout will mow typically consist of shrimp, immature dragonfly nymphs, leeches and zooplankton.

Shrimp are a staple diet item because they are available at all times of the year – though shrimp are not found in every lake. They require high levels of calcium in the water to maintain their chitinous exoskeleton. Lakes that have good shrimp populations are always very productive and have the capability to grow big fish.

Dragonfly nymphs live for up to four years before emerging as an adult. They can reach a very large size as a nymph and are actively sought by trout. Leeches are also present throughout the year. When fully extended they can reach 25 cm. in length. Certainly a mouthful for any trout!

Zooplankton are the almost microscopic "water fleas" that you see swimming in your glass of lake water. Daphnia and Cyclops are two common orders of plankton found in our local lakes.

Unfortunately the angler will have a difficult time imitating these minute food items!

Trout feed on daphnia and Cyclops because they are found at all depths of the lake and are easily filtered through the gills and swallowed. They are also very nutritious and help impart the deep orange flesh color of the trout.

It's important to remember that at this time of year, during the day, the shallow areas of the lake which are often associated with good fishing are too warm for trout. It is after the sun is off the water and the temperatures cool that the fish will actively feed. Big food items like dragonfly nymphs and leeches are very effective at this time.

Also associated with summer weather is the occurrence of off-flavored or "muddy" trout. This condition occurs in many of our local lakes, especially ones situated at lower elevations.

Muddy trout are not a result of a muddy lake bottom. They occur as a result of blue/green algae blooms which thrive under sunny weather and warm water. These blooms appear like a carpet of short yellowish/green grass clippings or spheres the size of small pin heads. They literally blanket the upper two to three meters of water but are thickest near the surface.

These blue/green algae release certain chemical compounds that are absorbed through the skin of the trout and accumulate in the fatty layer just under the skin. Trout will typically remain muddy until the fall when the amount of daylight and algae growth lessens and water temperature drop. Fishing during this time of year is often referred to as the summer doldrums. But understanding a little lake biology should improve your angling success.