Waterways Ireland is advising boat operators that a breach in the canal has happened in the vicinity of Richmond Harbour in Clondra.
They say the breach has resulted in a significant reduction in water levels between Locks 45 and 46.
No access to Richmond Harbour from the Camlin River will be possible until further notice, and no access to Richmond Harbour from the eastern side through Lock 45 will be possible until further notice.
Anyone with boats moored in Richmond Harbour is advised to check on the boats regularly as water levels stabilise and rise again.