>>2670491A lure generally takes about 1 second to drop 1 foot in water, depending on the weight. Toss out, count down until you hit the bottom, and it'll give you a rough estimate of how deep the water you're fishing is. There's also a more accurate technique of using a bobber with a heavy weight.
Alternatively, if your lake has a park, they might have charts available online or in the park headquarters.
A lot of lakes I fish have depth charts I can just google. It won't give you every nook and cranny but it's accurate enough.
If you're ABSOLUTELY autistic, you can get a castable fish finder for less than $150. It's overkill but just worth an honorable mention.
