Anguilla, Antigua And Barbuda, Aruba, Bahamas, Barbados, Belize, Bermuda, Canada (B) (P), Cayman Islands, Colombia, Costa Rica, Cuba, Dominica, Dominican Republic, Ecuador, El Salvador, Guadeloupe, Guatemala, Haiti, Honduras, Martinique, Mexico, Montserrat, Netherlands Antilles, Nicaragua, Panama, Puerto Rico, St Kitts And Nevis, St Lucia, St Vincent and The Grenadines, Suriname, Trinidad and Tobago, Turks and Caicos Islands, USA (B), Venezuela, Virgin Islands (British) (NB), Virgin Islands (U.S.) (NB).
Vagrant to Denmark, France, Greenland, Ireland, Jamaica, Japan, Netherlands, Northern Mariana Islands, Portugal, Russia (Asian), Spain, St Pierre and Miquelon (P), United Kingdom.
Central Alaska to north-western USA, and east to Great Lakes.
 
Population
Estimated population is 3,000,000 (2010).
Lesser Scaup (Aythya affinis) [XC284599]
by Richard E. Webster from Bowdoin National Wildlife Refuge, Phillips Co., Montana, United States (flight call)
Lesser Scaup (Aythya affinis) [XC871071]
by Stanislas Wroza from Arrondissement de Quimper (near Pont-Croix), Finist\u00e8re, Bretagne, France (song)
Subspecies
Considered by some to form superspecies with Greater Scaup (Aythya marila).