Frozen River

A frozen river is an ice topped variant of the river that replaces it in cold regions.

Frozen rivers generate in the same way as rivers do, forming long valleys below the sea level, cutting through inland terrain, but they only generate in the coldest temperature zones. Like rivers, they can form fjords or dry land depending on the surrounding terrain, and end abruptly far inland. Frozen rivers also replace swamp biomes in the frozen temperature zones.

Sometimes, frozen rivers can generate next to regular (i.e. non-snowy) taiga biomes, as these are able to generate in the same temperature range as frozen rivers. As a result, the central region of the river will be frozen over, but the edges have exposed water. Mojang have decided that this is completely intentional.[1]