Lake Serena "was the smallest, shallowest, and most biologically interesting of the chain of lakes skipping sporadically down the long rift valley south of Kareenburg."
Sergeant Penney and his wife Ma Penney had a home and dock there with a boat rental business. He'd done business with the Vorkosigans and Oliver Jole in earlier years before Jole acquired a large sailboat. When Jole decided to resume sailing with Cordelia, he set up an exclusive weekend just for the two of them.
While there, they enjoyed the use of a transparent canoe - excellent for viewing the interesting biology of the lake.
The University of Kareenburg had not completed their investigation of the creatures in the lake; this led to Oliver's eventual rebirth as a marine biologist.