View Full Version : thermocline and fish effects

08-22-2016, 08:38 PM
I used to scuba dive,and in the summer time in the lakes I dove at were at the deepest parts about a little over 100 ft. but the first thermocline was at about the 14 to 20 ft depth,depending on the time of year.I very seldom dove no deeper than 40-50 feet. there were very few fish at that depth. at the thermoclines you could hold your hand just above that line where you could feel a very big change in temp.so I know about thermoclines but I never thought about the effects it had on fish,and at deeper depths. the reason there were not many fish there because of the lack of oxygen.Now my queston is in a lake where the depth is less than 12 ft at the deepest part,and the outside temp.is almost 100 degrees and not much oxygen. Where do the fish go to get oxygen because the oxygen content of that lake is very low.I would think they would seek running water because it will help put more oxygen in the water.again where do they go.

08-22-2016, 11:22 PM
A lot of shallow bodies of water have a lot of vegetation which helps raise oxygen levels.Also if the body has a lot of boat traffic with outboards the props and boat wakes actually add some oxygen.And largely the phytoplankton are responsible for the majority of oxygen content. But if the water becomes unbalanced then the fish can die.Generally speaking though shallow bodies of water can be very healthy fisheries.And the ones that have vegetation like moss and grasses and lily pads etc will hold the fish a lot of the time.

A good illustration of what can happen in unbalanced shallow waters is cutoff flood waters. When the Mississippi floods it leaves behind small ponds and lakes. Sometimes fish get cutoff in them.These waters do become depleted of oxygen many times.The fish have no where to go...and they die...beginning with the fish which are most sensitive to low oxygen levels like game fish.The last to die are the gar and bowfin and similar species which are tolerant of low oxygen.

On the flip side in the major river systems where turbulence and current mix the waters...fish can and are caught in the deepest holes many times.It's very common to catch fish in say the Ohio or Tennessee rivers (especially dam tailraces) in the deepest water there. If the current is swift the fish will position in holes in the bottom or behind some structure to get a break from the current.Very common to catch fish at times in 50 ft of water or possibly more. When I use to snag paddlefish below Kentucky Dam many times they were on or very near the bottom of the deepest water...since they are plankton feeders ...plankton have to be there and and I am sure other bodies of water have oxygen producing plankton at deeper levels which have to be producing some additional oxygen..because occasionally fish of a variety of species are caught at depths of 40 ft or more in lakes.But it does vary from one lake to another and time of year and other conditions.

This is all just my observations ...

08-23-2016, 04:40 AM
Another thing is that smaller, shallow ponds/lakes have underground springs which help replenish the oxygen levels.

08-23-2016, 06:21 AM
Oxygen content in a shallow spot like a max of 12 foot may or may not be what drives the fish in there . They might just seek cooler water in the deep spots and get lethargic and just survive the onslaught from the heat . Not sure but if I was looking in a spot in the summer with a max depth of 12 and it was 100 outside
I would start there first for crappie ......

09-09-2016, 11:21 AM
My mother has a log cabin on a 350 acre lake with a max depth of 15'. This lake is in Northern Wisconsin and is pan-fish, muskie lake. There is a stream entering and exiting the lake in the shallowest part. That 100 acres part of the lake is full of weeds, its a big flat area about 5' deep. Spawning grounds. All the fish are caught everywhere but there. The rest of the lake is a big bowl with a sand bottom. Most of the fish are not in the deep cool section. They are in the cover surrounding the edge of the lake. Predator and prey use the cover for different reasons, to attack from and seek protection. One would think the fish would seek the coolest spot, however the instinct to live is stronger than the desire to be cool. Fish will adapt to their environment. Fish have basic needs for survival; oxygen, food, cover, etc. Know the body of water and how each species of fish accommodate their needs and you will find fish. There are no hard fast rules that apply to all species of fish.