About the site
One Tree Sinkhole is near some of the other famous holes in the Mt Gambier region, and gets dived regularly. The caves in Mt Gambier may not be as extensive or as decorated as those in Florida or Mexico, but the large and impressive sinkholes are truly world class. I’ve shown a few shots from Picaninnie Ponds and Kilsby’s Sinkhole which both have incredibly clear water. The clear water means sunlight and rays deep into the water. The less-talked about sinkholes in Gambier aren’t so clear.
On the greener side of the fence there are a few shallower caverns, like Two Sisters, Earl’s Cave and Goulden’s. The deeper holes include One Tree, Ela Elap and Little Blue, which is used as a swimming hole in the summer. All of these sites are open to the air and sunlight, and have varying degrees of algal growth throughout the year. In summer the top layer of the hole will often be particularly dark, stopping the lighting penetrating very far. The darkness means less algal growth in the deeper water, so as you descend you break into clear, dark water. Check out my last photo from One Tree, with almost no sunlight reaching the bottom.
In winter less sunlight restriction algal growth and can mean the green is lesser, but spread more evenly through the water column. The fine silt on the bottom of all of these holes is very easily disturbed, so whatever visibility you started with can rapidly deteriorate as a result of the divers in the water.
About the dive
This photo was taken on a recent trip over to dive in the sinkholes for a weekend with KA. My parents decided to join us at the last minute, which was fortunate when KA had ear problems on the Sunday morning. I was keen to get some photos to enter into the Underwater Festival. I wasn’t completely convinced that the green water and poor vis was going to produce the winners I was looking for. As we arrived at the site the water’s surface looked very clear and we didn’t encounter any real visibility change on the way down.
About the photo
It would be very hard to confuse this photo with one taken in Kilsby’s, and there was no point in trying to take the same kind of photos. The reduced levels of algae and clear sunny spring day up top meant enough sunlight was reaching the bottom for the camera to pick it up – just. Both of these pictures were taken at ISO800 and a shutter speed of 1/30th to bring out the green glow in the water that was clearly visible to the eye. In the main photo, the off-camera strobe that Mum is aiming with her left hand is lighting up the edge of her fins, increasing the contrast between yellow and green.
In a clear water cave, this wouldn’t be a novel photo. In clear water I’d be working hard to find a suitable roof, weed or sky combination to frame the diver. The green sun above gives an otherworldly impression and frames the diver in black where the sinkhole walls cut off the light. The bubbles up the side are a sign that shooting straight up is a lot easier with a rebreather….a discussion for another time.