In Finland they start to close rivers when water is +20 or +21 celsius, depens about river. This goes more to mid Finland, in here and more north they don't have this closing process yet, it is partly because rivers starts from lakes which can be deep and cold so there is oxygen in water. This is just excuse to keep rivers open and get license money coming in.
Nowdays most of the flyfisher are stopping fishing when temp gets over +20, no later than +21. or they just stop releasing, that's the other story anyway.
Other interesting fact is.... we have running trout here, it is coming thru long and narrow lake which has dephts more than 100 meter, so water in lake is cold, in surface it can get +20 but... in depth where trouts are coming it is more like 16 celsius or less, that means two things for running.
First if water temp in river is 2 degrees warmer than lake water, trouts won't start they run. They either wait on lake that river water gets cooler or that they adapt themselves for river temp. If temp in river is more than 19 celsius, they wait. Haven't heard or seen any new runners on those temp.
Rain and thunder always launch runs, it means always cooler river water and fresher air all the way, so river water can easily drop from 21 to 18 celsius and because of rain lake water is also changing the temp so it always launch the run. That's why after heat waves and warm river water, when heavy rains comes... river is filling with fishermen and running trout. Pressure to get spawing area has been rising while waiting, you might know that feeling from your younger days.
Also cool august nights are doing more or less same than rain. In here big even 8K brownies might run in less than knee deep water in August at dark, do not wade.
Mika,
close from Arctic circle
I do Nothing everyday .
)
