You can fish for perch and carp in the lake or for trout in the Riviyre d'Argent (Silver River), or just glide around the lake among the swans.
You can go fishing or watch swans in the river. 
mnli hypothesis: You can go fishing or watch swans in the river.  premise: You can fish for perch and carp in the lake or for trout in the Riviyre d'Argent (Silver River), or just glide around the lake among the swans.