I swear, the networks seem to have the same batch of ideas all at once. Ponder these two series: "Invasion" and "Surface". While you're at it, make the mistake of watching "The Abyss" and "Close Encounters of the Third Kind" in the same week. Then try - just try - to keep any of the details straight.
So far, I've seen lights from the sky drop into the water, lights from the water fly up towards the sky, people get taken over like "Body Snatchers" (or Goa'uld from SG-1), and compulsion to travel to the "main site". Gah! It's too many plot derivatives!