Up thirty feet and down eighty feet in the same year? If your reservoir regularly changes depth to manage water supplies or due to drought the daily, monthly, or yearly change in depth affects your fishing success. Or simply plays with your mind and tests your ability to find the fish every day.
Water management trumps fishing in all cases. In a chain of reservoirs along a water system some lakes stay full due to recreational prospects, depth, temperature, location, and a host of other reasons while other lakes are managed to rise and fall on a regular basis. Calling the powers that be in the area, watching published water information sites, or working with a guide can help you understand the past, present, and future of a specific lake.
Consistent success on a fluctuating reservoir starts with a clear understanding of the lake’s current configuration. To save time on the water follow these steps with a topographic map of the lake at home. For a fluctuating reservoir I will buy two or three copies of the same map (Fish-N-Map, Fishing Hot Spots, or similar) and fill each one out for specific water levels. I use Bic Mark-It fine-point permanent markers in pink, green, blue, and black to help me quickly understand potential fishing areas on a new lake. Highlighters in similar colors will work too but will not last if the map gets wet.
With the black marker I write the water level at the top of the map and then outline the new shoreline. Then I take the blue marker and outline the maximum depth I expect to find fish. For bass and walleye I often mark a line 30 feet deeper than the new water level. For lake trout I outline a light green line at 40 feet and then the blue deeper line at the 110-foot level. This process quickly eliminates about 60% to 80% of the lake.
With the yellow maker I follow the shoreline and highlight large flats in the 4 to 10 foot level while also highlighting long points that extend into deeper areas. I then take a pink marker and highlight deeper flats and points. I then use the black marker to mark any areas where the contour lines converge into a cliff-like area.
Immediately I know I need to cast the yellow areas and use sonar to explore the deeper pink areas. The black lines on the dropoffs often congregate fish so they need to be checked properly as well. Suddenly the adage of “10% of the surface area of a lake holds 90% of the fish,” has been identified.
If I need to refine my focus even further I look at the areas where the deep blue line comes close to the black shoreline. Fish often congregate in these areas before and after they move shallow. Then I sight-in the largest yellow and largest pink areas because the largest structure holds the most fish in any lake. This large area may be a point, flat, channel, or dropoff and in some lakes where none of these items exist the basin acts as the largest structure in the lake.
On the lake, take at least an hour to drive the points and drop-offs then cast to a few shallow areas before fishing in earnest. This habit will pay dividends in spades throughout the times when the lake levels change dramatically. After a couple of spots and a fish or two the first day a pattern will develop. Your map study will pay off again because when you find walleye at 20 feet on mud flats finding another mud flat with similar conditions becomes a snap.
The constantly changing lake requires a flexible mindset as well as a solid commitment to finding fish before fishing. With enough work these situations can make you a hero while all the other boats on the lake throw away casts in the areas the used to hold fish.