That’s an exciting sighting – thank you for sharing! Black swans aren’t native to Michigan, as they come from Australia, but they’re sometimes seen in the state as escapes from collections or waterfowl sanctuaries. The pair you’ve spotted are most likely from the Kellogg Bird Sanctuary in Augusta, which keeps black swans among its display species.

If you manage to photograph them again, that would be wonderful! Such records are always interesting to local birders and can also be logged on eBird as an escape or introduced bird.