2017 UPDATE from June 28: The road to access the beach is closed due to the flood!
Rouge Beach is relatively long and wide, with great sand, and it is equipped with changing rooms. It was a nice little "adventure" to get there. From the parking lot, we had to climb up stairs, cross over a bridge to get to a boardwalk (where we got a superb panorama of the lake). The beach looked like a seashore during low tide. The trail eventually took off from the edge of the cliff, so we came down the path to get to the beach itself. We saw many people fishing in the Rouge Marsh adjacent to the parking lot (accompanied by a large population of geese). Some were launching their canoes into Little Rouge Creek while others were canoeing back from Lake Ontario into the creek. Note that this beach is often unsuitable for swimming due to the many geese visiting this site.
(On my visit on June 28, 2017, the road leading to the beach was closed. Schools of tiny fish (or tadpoles) were swimming in the pond created by the flood over the road. Only people with canoes could reach the "beach" from the west side of the park. Based on a few photos seen on Internet of the access on the east side of the bridge, there's not much beach showing at this time.)