I noticed in the long grass, it has been flattened into circle. What causes this?

I'm not saying it was aliens...but it was aliens

Alligators spin in the grass to create beds to lay in.

The water from the river is what actually causes the grass to lay down as it gets older and weaker as the tide causes higher water levels. Although the Alien Alligator would make a great attraction its not really the cause.

Alien alligators? Lol