Salt water
The lake is technically a back-barrier seepage lagoon, one of only two in Ireland. The other is nearby Tacumshin Lake (Irish: "Loch Theach Cuimsin"). The lake has no outlet, but is separated from the Atlantic Ocean at the southern end by a sand and gravel bar 200 m wide. Salt water seeps through the barrier, while fresh water flows into the lake from run-off from the land around the lake. This means that the lake is neither fresh nor salt water but somewhere in between. Every so often, storms break through the sandbar and salt water flows in from the sea, increasing the salt levels considerably. Wildlife in the lake must therefore be able to cope with variable levels of salinity.