。
I can swim across the river.
Literal
I [topic-は] river [path-を] swim-[sequential-て] cross [nominalizer-こと] [subject-が] can-do.
泳いで渡る ('swim across') — the ~て form links 'swim' with 'cross.' Notably, 川を泳ぐ uses を for the path/route traversed — a distinct particle use where を marks the route of a motion verb (not the direct object of a transitive verb). ~ことができる is the explicit potential construction.