Mergus is a genus of ducks in the seaduck subfamily Merginae. For an overview of the duck, goose and swan family of birds, see Anatidae.

Although they are seaducks, most of the mergansers prefer riverine habitats, only Red-breasted Merganser being common on the sea.. These large fish-eaters have serrated edges to their bills to help them grip their prey. Along with the Smew and Hooded Merganser, they are therefore often known as "sawbills".

Species are:

• Brazilian Merganser Mergus octosetaceus
• Auckland Islands Merganser Mergus australis (extinct)
• Red-breasted Merganser Mergus serrator
• Common Merganser or Goosander Mergus merganser
• Chinese Merganser Mergus squamatus