This skill is exactly like Fishing, the only difirence is you actualy stand on the river.
The first step is to make a hole in the ice. There are two methods to do this. The first is to have a Giant use Stomp, and the second is to use Land Maker with a Snowfield L-Rod. The second method requires a Giant-allied human. Not all areas on a frozen waterway will necessarily allow a hole to be made, so you may have to move around a bit to find the right area. Once a hole has been made, you may start fishing, but the hole will close in 2 hours (real time). The Reus River is the only place to go Ice Fishing at present.
Due to this being in Vales, it is not easy for elves to get there. Once elves get there, they still have to have a giant or giant-allied friend to make a hole to fish.