There's a lot of grass in Franks Tract, and at low tide, it gets pretty shallow in some ares. I've even heard of parts of machinery (tractors etc.) sticking up through the surface, although I've never seen that myself.
Old river is usually pretty clear, except for the occasional LOG floating just beneath the surface. We were out yesterday, and there was a lot of floating reeds from the high tide, but seemed pretty clear of anything that would do any damage.