June 11, 2009
A greener lake
With Folsom Lake just a few minutes away from home, I really wanted to go back there diving. And I wanted to do that as long as the lake was still full, but the weather just wasn't cooperating. This is unusual for the Sacramento area where the weather forecast usually turns to "sunny and hot" in May and stays that way until October or so. I kept checking the water level of the lake at the California Department of Water Resources website and my dive gear was packed, but I didn't get to go back to the lake until June 8, a sunny Monday morning.
The lake level was at 461 feet or just about the same as on our last dive in the lake, which means 930,000 acre-feet, close to the capacity of 975,000 acre-feet. We paid our eight dollars for a day pass and parked at Brown's Ravine with no one else there but the park cleanup crew and a couple of fishermen. The dive plan was to follow the perimeter of the submerged parking lot, then go down the boat ramp at the lot's far side until we found its bottom. We had originally planned on making and deploying some kinds of markers that would be found once the water went down again, showing how deep underwater the marker locations had been. However, we couldn't think of a good way of doing that.
The water looked quite clear from the surface, amazingly so given that there'd probably been thousands of people swimming and boating over the prior weekends. However, as soon as we waded in we saw that the color of the water had changed. It now had a distinctly greenish cast compared to the blueish tint back in mid May. It still felt clean, though, without debris or algae floating around. Water temperature at the surface was 69 degrees.
As soon as we went under I saw that the visibility was poor, probably no more than five to seven feet. There was also considerably more silt and the yellow double line on the submerged road was barely visible anymore. We had resolved to stay close together so we would not get separated, something that can happen in an instant in murky water. Visibility was so poor that at times it was hard to even follow the perimeter of the road, and I wasn't quite sure I wanted to descend down the ramp once we found it as it'd probably be like pea soup there.
One thing we noticed was that the water had warmed up quite a bit. It was 70 degrees at the surface and still 68 degree down at 25 to 30 feet, whereas it had dropped to 57 degrees at that depth just three weeks ago, with a steep drop from 70 to 57 between 15 and 20 feet. Now the temperature didn't start dropping until we got to 30 feet.
Visibility at the top of the ramp was bad, but no worse than during the 20 minutes it took to get there, and so we decided to go down. It feels a bit weird diving down a deeply submerged ramp where you can barely see anything and it gets darker and darker. The temperature also rapidly dropped into the 50s, though it didn't feel very cold with the 7mm wetsuit, hood and gloves, and having started out in fairly warm water.
We found the bottom of the boat ramp at 83 feet -- which translates to an elevation of 378 feet -- where it ended in the silt. The temperature at 83 feet was 50 degrees. I took a couple of pictures while Carol explored a few feet beyond the end of the ramp. Anything farther than that and it'd have been too easy to lose the ramp and then simply be at the murky bottom of the lake, without anything to orient yourself by.
The much lower visibility meant we saw fewer fish though they were clearly there. We did see what seemed like millions of tiny fry. First I'd thought it was just floating debris, but it was schools of little fish, everywhere.
I was surprised at how much more silt had accumulated on the bottom within just three weeks, and so we were careful not to touch bottom with our fins and stir things up. This meant staying close enough to the bottom to see where we were going, but not so close that we touched and caused silt-outs.
We made our way back up the ramp, following the steel cable in its center, and then onto the parking lot where we used the compass to cut across the lot and back to our starting point. On our prior dive the water had been clear enough to explore a bit, but this time it was just swimming in a greenish world that disappeared a few feet away from us in all directions, and all we could do was follow one another.
It was a fun dive nevertheless, and I was happy that we found the bottom of the ramp. But it was amazing to see how quickly the water had gone from fairly clear to quite green. The much higher water temperature in the top 20-25 feet probably facilitated algae growth.
The moral of the story is that if you want to dive Folsom Lake, do it as early in the year as possible, when the new water from the Sierras is still cold and fresh.