And don't assume a river is worse than a lake... I've got a couple lakes near me that are notorious for having little pockets of very thin ice or open water, while the rest of the lake might be 18 inches thick. There are numerous springs under the lake that feed water into it, and can slightly warmer water to bubble up.
1) 2000 Arctic cat ZR 700, which now thinks it is a 2001 ZR 600 EFI APV w/136" ripsaw. (for sale!)
2) 1995 Yamaha VMAX 600, which now thinks it is a Polaris! (Polaris x10 suspension, Polaris P85 clutch) (for sale!)
3) 2004 Yamaha Warrior
4) 2006 Yamaha Nytro