This is a square painting of marshland/wetland with trees and seagulls in the skies.
The colors are very vivid, the painting is signed "Matson" in the lower left corner.
After doing some research, I think this signature belongs to an American artist Richard Matson.
This painting is likely to be a "plain air" piece, as there is some paint on the back of the board. Not sure if it belongs to his Key West series.
I also think this piece is vintage, as the frame looks old.
Please notice that in the middle of the painting there is a spot that looks like somebody placed a piece of fabric on wet painting. See pic for close-up of this particular spot.