Exquisite Biome - an ecosystem-crafting game

Oooh actually just had a thought to tie all this together - we could be looking at a particularly large glacial valley, so with a particularly wide river bed that's spread/grown in volume with late spring snow melt you could have a (temporary!) island in the middle of that, formed from particularly large debris washed downstream.

Oooh I love that! A floodplains or river delta kind of situation, but much colder than we normally think of those places.

I think we shouldn't restrict ourselves to just the area on and around the island though -- it's a feature, but probably not large/isolated enough to have its own unique biosphere.