This is the rising of the River Shannon, taking water from Shannon Cave and other sinks on Cuilcagh Mountain. It was first dived in April 1971 by J. V. Elliot and Roger Solari, who reached a depth of -6 m at an overhang with a black hole below. Returning in September 1971 they reached -8.4 m to find the water emerging from a long slit 150-300 mm high. Martyn Farr dived in April 1972 and confirmed the previous findings but got no further. In 2009 Artur Kozlowski broke through into a large submerged chamber, the floor of which is at -14 m. This is quite unstable.