Originally posted by i have 2024 vision fear me:

But anyways, it is pure RNG, but the best chances to find one is in deep swamps. If they're long but narrow, then it's pretty unlikely to find any, but your chances are better in thicker type of swamps. Of course, you first got to find and explore them, so, not the most useful advice.

I think you are correct - the long narrow ones tend to come up empty. Not ALL the time, but as a tendency for sure.