We still have gales, very high tides and swells. This gull was having a hard time flying when I visited the track where vehicles enter the beach. In the video, at about 13 seconds, you can see it was blown backwards. 🐦

The brown sea / river water is likely from churned up sand.

Gull with wings spread over fast-moving brown water.
Gull with wings spread over fast-moving brown water.
Gull with wings spread over fast-moving brown water.