Not a big off, but I thought I'd post it nonetheless, for if I had read about it beforehand, it wouldn't have happened to me. Riding off road in Southern California near Big Bear, there are many stream crossings. The ones that are natural are no problem. The ones that are a concrete road with water running over them can be. I don't ride fast, and as I rode at 5 mph through this little 2 inch deep 4 foot wide creek gently flowing over the concrete road I was thinking what a lovely day it was, and how warm it was, and why then did it feel like I'd just hit a patch of ice? And as the bike slooowly rotated out from under me, and I put my hand in the water, and then less than gracefully exited stage right into the bushes, laughing my butt off the whole time, I realized what had happened: Algae. Green slime covering the road as slick as (insert favorite personal euphamism here). Never enter a water covered flat surface in a turn of any kind. Here endeth the lesson I wish I had known Saturday morning.