How to map a billabong

I just checked out the Wiki page on waterways and was surprised there's no tag value for a billabong. These dead river arms usually occur in naturally flowing rivers when a tight loop is cut off in a flood and develops into something that looks like a section of river from above but more like a lake on the ground. When rivers are artificially rerouted, there can also be longer stretches that become stagnant like this.

It seems these are usually mapped simply as rivers, but I suppose to somebody using them as a waterway their lack of current and the tendency to become overgrown and shallower over time would make quite a difference. Completely cut-off sections could be mapped as lakes, but that requires drawing a complete area instead of just a line with a width tag.

Any opinions on or other possibilities for that?