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.
These bomber emergences usually occur during the warmest period of the summer and they can be found hatching in water anywhere from 10 to over 30 feet in depth. This emergence can be fished with floating lines and strike indicators, floating lines and long leaders and no indicator and with intermediate to type 7 sinking lines. Choice of line type is dictated by the depth of water that the chironomids are emerging from. However, in the majority of situations the most effective technique is to suspending pupal patterns under strike indicators. Indicators are set so that the pupal pattern is hanging within 12 to 16 inches of the lake bottom.
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.
Fishing big larval or pupal patterns under an indicator and potentially long leader can lead to casting frustrations. To maximize fishing time and tangled leaders try and keep your casts short, less than 40 feet is fine as you want to be able to see any movement of the indicator. Try a RIO Grand or RIO Indicator II line as they both are effective at casting indicators and multiple fly rigs or a swivel and a single fly. A couple of roll casts is often all that is needed in this type of fishing. Watch for your indicator and fly combo or swivel and single fly to hit the water in their proper order. Strip in, check and re-cast before any tangle gets worse.
Watch for this special summer time emergence next time you are on your favourite reservoir fishery.