Circular features along the Nile Delta. Is this some type of agriculture/farming?

I've found more circular features similar to these off the coast of Florida via NASA World Wind
Also seen in the Modoc National Forest in California and off the Coast of North Carolina.

when I first looked at these I thought they might be mangrove trees planted in some sort of water quality restoration effort of the lake, but the longer I look at them I think they are reed beds. The uniformity of the spacing certainly makes it look like they were planted on purpose, which could mean that they are being harvested commercially.