Sans slicing your finger open on a hook or drowning, falling into a cold creek is easily one of the worst ways to ruin your day of fishing. I grew up fly fishing the limestone streams of Central Pennsylvania and can’t begin to tell you how many times this happened to me (Spring Creek, the Falling Spring, and the Letort around Carlisle can be wild to wade/walk in). That water is probably no warmer than 56 degrees, which means you’re sitting around slowly getting hypothermia while your boy tries to land a trophy brownie.
Getting water in a leak wader sucks enough. Going completely under sucks even more.