confused??

byf

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I have been fishing a stream the last couple of weeks. There has been a wonderful caddis hatch every evening at 730. The fish had been consistently small so I decided to try a section where I usually find larger fish. I arrived around 7 and fished until almost dark and not a bug in the air. When I left I crossed a bridge downstream and there were bugs everywhere. Any idea why? The sections of stream are separated by a 25 acre lake.
 

Ard

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Hi,

Since I don't know the geographic region you are writing from I will take my best guess. There are many conditions that can lead to either the presence of or lack of the presence of aquatic insects and you have noted a lake separating 2 sections of a stream. I should also state that I am in an age bracket which allowed me to dry fly fish focused on Mayfly populations and seldom paid attention to caddis flies which have become much more prevalent over the past 30 years in some parts of North America.

Best guess number one is water temperature. The outflow water from lakes is naturally warmer than waters of a free flowing stream due to having been impounded. Between solar heating and atmospheric temps the water will become quite warm at and near the surface and that warm water will make up the bulk of the outflow. Your caddis flies may be intolerant of certain temperature conditions and so do not exist in the area.

Best guess number two is related to the oxygen content of the outflow water. Low oxygen levels may be related to several conditions, low gradient flow, temperature are the 2 prime suspects in your case. The makeup of the creek bottom downstream of the impoundment can also be involved. If your caddis prefer gravel bottom and swift flow your bottom may be holding more silt. Silt can be just varied mineral deposition or if the lands around the lake / impoundment are heavily developed the deposition can contain any number of contaminants related to runoff water from developed land which is collected in the lake.

To get a better understanding of how lakes behave in temperate zones just google Lake Turning Over. Those words should lead to some info on how impounded water reacts to seasonal changes. For the near future I would just fish upstream from the lake or well below the bridge where you witnessed all the 'bugs'.

Of course there's a chance I am wrong on all counts but you ask.
 

byf

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The area is the Black Hills of South Dakota. The upstream section flows from a large lake with bottom discharge dam but is 9 miles above the smaller lake which has a top discharge dam. The stream bottom is pretty consistent in both sections I will have to take temp readings from both sections. The upstream section has very little in the way of population or ag and the downstream section runs through town.
 

Ard

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Between the water temp of the outflow, top flow lakes are often quite warm, and the actual character of the water may be the answer. By character I mean current speed riffles and such. I've seen some very attractive places (visually) that were pretty devoid of fish and that generally relates to the intrinsic properties of those areas.

Here in Alaska there are many streams and some rivers that look like they should be crawling with rainbows but they are basically sterile other than when hosting migratory fish. I don't dry fly fish here unless I do an August Grayling trip to specific rivers. Otherwise I fish with streamers all the time and interestingly enough catch large grayling on the big flies. Gonna go fish a bit today so I should get off here.............
 

silver creek

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I have been fishing a stream the last couple of weeks. There has been a wonderful caddis hatch every evening at 730. The fish had been consistently small so I decided to try a section where I usually find larger fish. I arrived around 7 and fished until almost dark and not a bug in the air. When I left I crossed a bridge downstream and there were bugs everywhere. Any idea why? The sections of stream are separated by a 25 acre lake.
I think I know why - it usually boils down to 3 things:

A. Water temperature
B. Water pH
C. Habitat - this means riffles for high oxygenation which are aquatic insect factories.

So here's a suggestion. Take readings and examine the areas.

1. get a thermometer and take the water temp at the same time in the areas.

2. Get some litmus paper or a pH meter and take the pH of the water in both areas. The area that is more alkaline (higher pH above 7.0) usually is more fertile for insects.

3 Finally examine the habitat and pick up some of the rocks and vegetation in the stream and see which area is richer in aquatic insects.

I think it is best to go examine the source when these types of questions arise,
 
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