Question: Lake stratification?

[OldBaldGuy]

Summit Lake - Largemouth bass fishing should continue to be good... Anglers should be aware that many lakes have stratified, so they should not fish in the deepest water and will probably find that bluegill, crappie and other panfish will be suspended at some depth. The best fishing will probably be in the mornings or evenings rather than during the heat of the day. (from NGPC’s August “Outdoor Outlook”)

I’ve been under the impression from several things Daryl has written in the past that stratification – and the subsequent fall “turn-over” – are largely limited to deep sand and gravel pits and to the larger reservoirs. Do lakes the size of Summit (or Zorinsky, or Burchard) stratify for prolonged periods each summer?

This leads to a second question: generally speaking, how deep is the thermocline? Does it vary widely from lake to lake or is it always found at about the same depth in each area of the state? Can you boat fishermen with sophisticated electronics see the thermocline on your screens?

And a third: Twice in the last two weeks, first with Catfishsteve and later with Aaron Lee, we found bluegills suspended at Summit between 10 and 12 feet, but Aaron’s graph showed few if any deeper than 12. Are they relating to the thermocline, water temperature, oxygen content, something else, or “all of the above” when that occurs?

[Alex T.]

having problems in non-feeder lakes?? I can only imagine the length of PM your'e about to receive.

Alex

[BoB_25]

Originally Posted by Alex T.

having problems in non-feeder lakes?? I can only imagine the length of PM your'e about to receive.

Alex

Wow, what a firecracker, you can tell you really need to shoot some Sky Carp!!!!!!!!!!!!!!!

[AnglerX]

That's the I and E dept for you. Which ironically stands for

Information and Education.

[Alex T.]

I'll be shooting birds on Monday and life will be all good again. Been too busy lately keeping OBG's stock prices going strong to get any real fishing in.

Alex

[BoB_25]

Originally Posted by Alex T.

I'll be shooting birds on Monday and life will be all good again. Been too busy lately keeping OBG's stock prices going strong to get any real fishing in.

Alex

[Greyelk81]

Dang good questions! ...I see Sam definitely rubbed off on you!

Too bad others would rather put holes in the sky instead of pondering the value of your thoughts.

Now I await my demise from all the hunters who shoot geese over my head when I'm fishing. It does make for a messy boat!!!

[CanoeGuru]

I can tell you from personal experience that the thermocline in the I-80 sandpits with depths of 20-25 feet is at about 12 feet right now. We were scuba diving out there again this past weekend. Saw quite a few little bluegill and a small bass or two. The highlight was a huge crappie I was fortunate enough to catch a glimpse of. All the fish seemed to be above the thermocline.

[OldBaldGuy]

Received this message from Daryl late today:

I’ve been under the impression from several things Daryl has written in the past that stratification – and the subsequent fall “turn-over” – are largely limited to deep sand and gravel pits and to the larger reservoirs. Do lakes the size of Summit (or Zorinsky, or Burchard) stratify for prolonged periods each summer?

Water has different densities at different temperatures and that is why it can stratify into layers that may not mix for the entire summer. Most Nebraska waters are wind-swept enough that they do not stratify during the summer. Even some of our largest reservoirs do not stratify during the summer because the wind blows hard enough to break up any stratification that might begin for a day or two. Surprisingly sandpits are the Nebraska water bodies most likely to stratify because the pumping that created the sandpit creates a relatively deep body of water. Couple that with the fact that sandpits are relatively small and often protected by lots of trees and stratfication commonly occurs.

Zorinsky? Burchard? Summit? Nope, no stratification. Those waters may begin to stratify on a hot, calm summer day, but as soon as the wind kicks up a day or two later--no more stratification.

This leads to a second question: generally speaking, how deep is the thermocline? Does it vary widely from lake to lake or is it always found at about the same depth in each area of the state? Can you boat fishermen with sophisticated electronics see the thermocline on your screens?

How deep is the thermocline? It depends! Depends on the water body, water levels, inflow and outflow rates, weather patterns, etc., etc., etc. No, the thermocline will not necessarily be near the same level in different water bodies in the same area of the state. On waters that do stratify the thermocline very likely will not be the exact same level from one year to the next. For that matter, depending on a lot of factors the thermocline can actually move throughout the summer!

I have seen sandpits where the thermocline was so shallow that you could float in the middle of the pit, extend your toes down as far as you could reach and feel the difference in water temperature! A thermocline as shallow as 6-8 feet is not unusual in sandpits (By the way, most sandpits have little or no oxygen below the thermocline in the summer and therefore no fish below the thermocline. If you think fishing deep water is your best bet during the summer, well, good luck to you, there may literally be NO FISH deeper than 6 or 8 feet!)

Yes, the thermocline can be detected on depth-finders. Since there is a change in water density in those lower layers, you may be able to detect that on the depth-finder screen. In addition plankton and baitfish may concentrate at a level corresponding to the thermocline and those organisms can be seen on a depth-finder.

And a third: Twice in the last two weeks, first with Catfishsteve and later with Aaron Lee, we found bluegills suspended at Summit between 10 and 12 feet, but Aaron’s graph showed few if any deeper than 12. Are they relating to the thermocline, water temperature, oxygen content, something else, or “all of the above” when that occurs?

How about "none of the above"? When bluegills are suspended in open-water during the summer they likely are out there following swarms of zooplankton. Zooplankton relates to the phytoplankton or algae and the level that algae is suspended at depends on the level of light penetration.

I am not saying I know that for sure, but that is the first thing I would suspect.

Later,

Daryl Bauer
Lakes and Reservoirs Program Manager
Nebraska Game & Parks Commission
daryl.bauer@nebraska.gov