Hedgehogs can swim, but will eventually tire and drown if they are unable to escape from the water. Swimming pools should have a plank of wood on the surface on which the hedgehog can climb to await rescue. Ponds should have an escape route fitted to the the side of them, these can be made with chicken wire or make a ramp the hedgehog can use. Don’t make this too steep, as it could get slippery when wet.