Lake turnover is an interesting phenomenon typical of most lakes that experience winter ice-over conditions. The best fly fishing lakes in the Kamloops area are no exception.
There are two times during the year that small lakes experience "turnover", in the spring and in the fall. In most cases, it's the spring turnover that is of most interest to the fly fishermen who are dying to get going with their season.
So what is Lake Turnover?
Lake turnover usually occurs 1-2 weeks after the ice comes off the lake in the spring. The sun melts the ice and warms the surface water until it eventually reaches it's most dense state st 4C (39F). This most dense or heavier water now follows the laws of physics and wants to sink to the bottom. As it begins to sink it displaces the less dense water below causing a complete flip-flop of the water column in the lake.
In the fall, lake turnover occurs before a lake freezes over. The air cools the upper layer until it reaches it's most dense state and then drops to the bottom. The lake then continues to lose heat and as the temperature dictates, the lake finally freezes over.
Why is this of concern?
In both cases "the turnover", combined with wind, is natures way of re-oxygenating the water. Both winter and summer seasons induce layering of water creating temperature bands (called thermocline). This lack of oxygen can be determinant to fish and in many cases causes winter kill or summer kill of the fish. The mixing of the water created by the turnover and those welcomed spring and fall winds, re-oxygenate the water to healthy levels critical to fish survival.
Turnover is quite an event for the body of water in which it occurs. It stirs up the lake bottom creating floating decayed vegetative debris and drastically increases the turbidity of the water. Oxygen levels decrease for a short period and the fish usually turn off from feeding. This event usually last from 1-2 weeks, depending on the wind. When the turn is done, the oxygen levels rise quickly and the fish, god bless them, get hungry and start to feed again.
So, if you come across a lake in the spring that looks dirty and full of debris, take note and get the heck out of there because you will most likely be wasting your time. Go back there in a couple of weeks and you may enjoy some of the best fishing of the season.