So Dave Shearer emailed me back after describing to him the two columns of bubbles coming up from the bottom of the GSL. He said they very likely were evidence of an underwater spring. He was interested in getting the GPS coordinates. I could kick myself because I cleared my GPS track yesterday, which I typically do when I start a swim in order to get a reset distance for the day.
So I got off work a little early this afternoon and went out there. The sun was shining and the wind was blowing slightly just enough to give a 2-3 inch swell. Not flat, but it was good enough to go looking. I took the same path as last Saturday and the water was clear enough to see the bottom which was good. But I was unable to find the spring. I started to back track, this time doing breast stroke and looking for any bubbles at the water's surface. Still nothing. Spent an hour and a half out there looking, and when I got back my GPS said I covered only 1.6 miles. It's like looking for a needle in a haystack.
From now on, I'll be swimming this route, but no longer going to do heads up breaststroke. If its meant to be found again, I'll find it while doing a training swim.
Total: 1.6 miles in 1.5 hours