Some of the most productive stillwater trout fisheries found in the western states and provinces double as irrigation reservoirs for the ranching and agricultural community. These impoundments can vary in size from a few acres to well over a thousand acres. The majority of these reservoirs are situated in arid regions which means long, hot summer growing seasons. Many are shallow in nature resulting in significant amounts of shoal or littoral zone that offers prime aquatic invertebrate and trout habitat. Some of the more common trout food sources found in these impoundments include scuds or freshwater shrimp, chironomids, leeches, damselflies, dragonflies and caddisflies.
By mid-summer the majority of aquatic insects have emerged or hatched. Water temperatures are warm and the trout seek the cooler water along the edges of drop-offs and into the mid-lake deep water areas. The hot summer period also sees more intense use of water for downstream use. Water control structure on these reservoirs are usually designed to take water from the bottom of the lake. This movement of water through a reservoir as it is being drawn down creates a current or flow of water over the benthic areas of the lake. The movement of water through the lake and accompanying dropping water levels often stimulate mid-summer chironomid emergences. Anglers that fish these often prolific fisheries look forward to these hatches as they can be very intense. An added bonus is the emergence of some very large species of chironomids whose larval and pupal stages can reach in excess of ¾’s of an inch in length. Seasoned chironomid anglers refer to them as bombers.
On really windy days anglers should watch for chironomid larvae or bloodworms floating in the surface film. These have been dislodged from their larval tubes by the combination of currents moving across the benthic areas and mixing of the water from the wind action. Seeing these larvae in the water column and floating on the surface means there will be some good bloodworm action.
Watch for this special summer time emergence next time you are on your favourite reservoir fishery.