May 18, 2016

Hot Summer Conditions and Stillwater Trout

The arrival of hot summer weather brings many changes to fish behaviour in the local fishing lakes. Fishing during this time of year is often referred to as the summer doldrums. But a little understanding of lake biology should improve your angling success.

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, we must understand the changes that are occurring within the lake itself. The sun has warmed the shallow areas of the lake and 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 to cooler depths where both temperature and oxygen levels are more ideal. Thus the diet of many trout in the summer will 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. However, they are not found in every lake as 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.

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

Zooplankton are the almost microscopic "water fleas" that you see if you fill a glass with lake water. Daphnia and Cyclops are two common orders of plankton found in our local lakes in BC. 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 colour of the trout. Unfortunately the angler will have a difficult time imitating these minute food items!

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

Also associated with summer weather is the occurrence of off-flavoured or "muddy" trout. This 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 due to blue/green algae blooms which thrive in warm water under sunny weather. These blooms appear and blanket the upper 2 to 3 metres of water like a carpet of short grass clippings or spheres the size of small pin heads.

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 algae growth lessens and the amount of daylight and water temperatures drop. 

While fishing during this time of year can be more challenging, these tips should improve your angling success.

Author: Brian Chan, Fishing Advisor, Freshwater Fisheries Society of BC
Photo Credit: Jim Wolf