The town of Yarmouth has several public beaches, and I certainly don't care for the $14 parking fee that's already in effect in June. The next town over, Dennis, doesn't collect parking fees until July. -- Regardless, if it keeps the beach open without busting the town budget, so be it.
I like Seagull Beach because it's secluded and quiet and still has a bit of Nantucket Sound wilderness feel about it. There are public toilets but no other services. Bring your own food. Also a nice ride down quiet back roads, if you're on a bicycle trip.
Behind the beach, on the other side of the parking lot, is the Swan River salt marsh. You can smell that briny stretch of nature as soon as you arrive on the parking lot. I do hope this salt marsh won't get paved over with new development! I've already seen some brush clearing closer up toward Rte 28 and it makes my heart sink. On any morning, you can do some bird watching there, taking a paddle boat tour down the Swan River.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.