King County in Washington state operates buoys in Lake Washington and Lake Sammamish that gather data at different depths on a regular basis. This is interesting for fishing because some of that data is important to the fish – and therefore to us as anglers. Specifically water temperature and oxygen content will affect where the fish will congregate.

This is especially true during the summer and fall when the thermocline develops. The thermocline is a layer of water where the temperature rapidly changes from the hot water above to the cold water below. It can serve as a barrier to the water above and below mixing, which then affects the oxygen content – as oxygen from surface interactions can’t get below it.

What happens is for species like trout and kokanee is that the water below the thermocline is a comfortable temperature, but doesn’t have much oxygen. The water above has plenty of oxygen, but is too hot for them to survive for long. So the fish hang out near the thermocline – sometimes going above it to eat or below to cool off.

There are different ways of determining the thermocline, but these apps make it easy and take out the guess work. Simply fire up the app and see where the thermocline is (it is where the temp and O2 rapidly change). Then just make sure your gear is fishing in that depth – which can be as easily as lowering your downrigger to match.

It really does work. In September I was out on Lake Sammamish with some friends. I fired up the app (then in development) and saw the thermocline was at 30’ deep. We let out our lines, attached it to the downrigger and lowered them down. One just above the thermocline at 28’ and one just below at 32’. 10 minutes later we landed 2 nice fish.

The app is available for Windows 8 devices and Windows Phone (7.1 and newer).

Hope you find them helpful.