A number of years ago a group of friends and I were diving a coastal cave. Really strong spring. Like 'hold on for dear life' type of spring. Not some Ginnie Springs Jackson Blue Little River spring, but the real f*&(%#' deal low vis, blow your mask off type. Its also lined with oysters, its deep, and its BIG. In hindsight, its a stupid location and I don't have any intention of going back. Ok story time:
On this particular dive day, it was the highest high tide of the month. Perfect. Flow will be down and this thing will be divable! We had a short window to set up deco gas ~20, 70, and 120, and the A Team was going to scooter in, lay some line, then boogie out with the flow at their backs and be back in OW before it got unmanageable. One of the guys had ear problems so they aborted the dive super early at 40ft.
Time to pack it up and go home :(
Getting in required hitting the spring at an angle in addition to dumping all the gas from your wing + a dropweight or two. My buddy and I head back to 120 via this oblique approach and we made some really good time getting there. Slick. We clipped off the 120 bottles and a scooter then turn for the door. But we aren't going anywhere. Stopped dead in our tracks in ~5ft of vis. Suspended particulate was blowing past us INTO the cave.
The now siphoning flow is getting worse and worse. You know how sometimes you can hear the rumble of the flow? That was happening. We wore leather work gloves to protect our hands from the razor sharp oysters. Pulling ourselves along, the oysters were breaking off at every handhold. Hearts are racing, gas is dwindling. This was probably our 3rd drop into the cave (120 wasn't far from OW) but we thought we had plenty of gas to get in and pick up a few scuba tanks. We were not prepared for this situation at all. We ditched the 120s and the scooter to reduce our profile in the water and make some progress.
I caught a glimpse of my buddy's SPG. You know that 'red zone' on some gauges. Yeah. The needle was FIRMLY in the red. The gas was low but the pucker factor was to the max. The lack of reasonable forward progress + possibility of getting blow off the line into the void turned our minds to mush.
Just as my reg got hard to draw from we hit OW, pointed the fins to the depths and up we went. Neither of us had to turn off the tank valves to get our regs off that day.
I took some lessons home that day. If you even think for a SECOND that you're thin on gas, don't do the dive. Things can go sideways in directions you didn't anticipate. Also take some extra time to do more homework on the cave you're planning on diving. None of us there that day knew that this cave siphons from time to time, but it turns out some other folks we knew were aware of it. Ask around. This is a pretty extreme example, but something much more simple (and common) is a blind T or a small reach gap. Easy things to miss that can sink your battleship if you're having a bad day on exit.
