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Location: MN | Are rivers with a decent flow safe to fish when the water temp is 80+? I would think the dissolved oxygen levels would be much higher in a river even in warm temps, correct? I have some small rivers in northern MN and WI I am thinking of fishing once the temps get too hot in the lakes, if it is safe for the fish. |
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Posts: 1828
| Haven't studied it or anything, but just thinking out loud:
I think at the tails of rapids and falls, etc. you might have good oxygen levels due to air entrainment from turbulence. But in stagnant pools, or slow-current stretches I don't imagine the oxygen content is any better than that of warm lake water.
In my mind, current alone does nothing to heighten O2 content, only mixing with air can bring in more.
Just my thoughts, again, not claiming to know for sure.
Do any of your rivers have temp gages? I think very few do, unfortunately. |
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Posts: 323
Location: Elk River, MN | Rivers would definitely be a better option than lakes of the same temp, much higher dissolved oxygen content. Just need to practice the same caution you would fishing on lakes of warmer temps. You be the judge if you think it's safe or not. Decent flow is key, slow moving water obviously would have less oxygen
Edited by Espy 7/20/2016 8:52 AM
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Posts: 815
Location: Waukee, IA | It won't raise the disolved O2 much at all outside of just below a spillway or major rapids. Still pretty dicey above 80 degrees. |
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Posts: 1425
Location: St. Lawrence River | On the flip side the fish have to spend more energy staying correct in that current as opposed to a more settled lake. This can put a tired fish at a disadvantage. |
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Posts: 300
Location: Minocqua, WI | Dams and spillways, not so good and would be a disadvantage. Warm water builds up, and what's trapped spills through. Natural riffles and current areas are on the other hand beneficial and fish attractors during these times.
Consider inflows, and especially if they're trout streams. Good chance these will be cool water sources. Fish will find these inlets.
If I have a water temp of say 78+ on my favorite small to medium current gradient river, I just won't bother fishing it because I know how rapidly water temps can rise and cool over the course of a 12-24hr period. Regardless of D.O. levels, I won't play with fire during a heat wave on any small flow. |
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Location: MN | Thanks for the replies. I would think a river would have more dissolved oxygen even if away from a spillway or Rapids. There are lots of places for oxygen to mix in for example down trees, exposed rocks etc. Does the 80+ rule only pertain to oxygen levels or are there other concerns for the fish? |
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Posts: 815
Location: Waukee, IA | Water physically will not hold enough oxygen above ~85 degrees for muskies to survive. Adding stress from C&R is where the 80 degree "rule" comes from. Even below an oxygenating landmark (rapids, dam, etc) the PPM will only be marginally higher than slow areas. Rivers and lakes are almost no difference in O2 levels at the same temperature. |
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| Nershi - 7/22/2016 11:24 AM Thanks for the replies. I would think a river would have more dissolved oxygen even if away from a spillway or Rapids. There are lots of places for oxygen to mix in for example down trees, exposed rocks etc. Does the 80+ rule only pertain to oxygen levels or are there other concerns for the fish? Hypoxia (lack of oxygen) is the primary concern, but even if the fish swims away after release, lactic acidosis caused by a buildup of lactic acid produced during the fight can kill them. The lactic acid levels produced in their blood in warm (low oxygen) conditions is enhanced because oxygen is necessary to mediate the lactic acid levels, and this excess lactic acid can cause mortality hours after release. See, for instance http://newmexicomuskiesinc.org/8.html |
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Location: MN | Thanks guys. I probably won't be able to fish much this weekend if that's the case. |
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