Yellow Pintail

This pintail’s chest should be white instead of a weird yellow-brown. Is that normal? Is it moulting or something? Or is it just swimming in dirty waters? I dunno

(I’m leaning towards the “dirty water” theory because as you can see, the neck and head are still white.)

   11 February 2023
   1/200s    f/7.1   175mm   ISO 640
Northern Pintail