The Marsh Sandpiper is a distinctive, very long-legged wader, with a fine long bill and small body. When not breeding, the Marsh Sandpiper has a soft grey-brown upper body, with breast and neck white. A white 'eyebrow' shows above the eye. When breeding, the head and neck are heavily streaked dark brown and the flanks and lower breast show bars or chevrons. The very long legs are yellowish green. Juvenile Marsh Sandpipers have more heavily patterned upper parts than non-breeding adults. When feeding, this species is very upright with slow graceful movements breaking into quick dashes. In flight it shows a dark outer wing and slightly lighter inner wing, and a white wedge on the lower back and rump, and its long legs trail beyond the tail.