gon2seed
(and me! - Ed)
Mystery solved! Was down there ( https://www.google.com/maps/place/S...ata=!3m1!1e3!4m2!3m1!1s0x0:0x1b47b3d511d85808 ) with my dog and she went in the water for a drink by the outflow Tunnel; what should charge out of the large outflow pipe but a hissing, flapping parent swan, closely pursued by three cygnets, so that is where they have been hiding!