Lake Havasu is a large reservoir behind Parker Dam on the Colorado River, on the border between California and Arizona. It's an active destination for a wide range of people, and during the winter months, the community is joined by retirees from colder regions of the country and Canada. Side note: the actual real original London Bridge, from London, England now lives in Lake Havasu. So if you wanted to retire in the U.K. but just don't want to leave the US, maybe Lake Havasu would do it for you. Better weather.