I've been fishing the Brazos for many years. Some years back, during the drought, the river was silted and full of moss, low water of course, and hot water during the summer. In the silted areas you would occasionally find some very small leeches attaching to your skin, not many, not often, and tiny ones. While they stick onto the skin they appear to be too small to penetrate through the skin. At least I've never seen a hole in my skin afterwards from them.

This year I've been getting a lot of the small leeches, but now in clean gravel bottom areas with only a tiny amount of silt.

Yesterday I had a leech over 1/2 inch long attach to my foot, out in the gravel area. Water temp is 85, river is low and has been for a while. Slight amount of silt over the gravel, really slight.

I'm wondering what is going on? Is the leech population exploding? Never saw one anywhere near as big as the one I had on me. I had the usual amount of the smaller ones too. Should I have kept it and turned it in for a record? I put salt on it when I got home, and it dropped off after a few moments. This one was under the strap on my sandal and rode me all the way home, walking, on dry land, for about a quarter of a mile after exiting the river. Tenacious bugger.

Any clues?

From what I've read they do not transmit human diseases.

I've noticed that some seasons seem worse than others for them. A certain river I fish, I've gone a whole season and never picked a leech of anything, then other years I've had to pick several of them off waders (and me) on virtually every trip.