Lake Powell is the body of water held back by Glen Canyon Dam in northern Arizona. There are other lakes named Powell, but this is the largest and most well known. There is a group out there called the Coalition to Rename Lake Powell who wants to rename it to Glen Canyon Reservoir. They state that this is because it isn't really a lake, but a man made reservoir, and that there is another lake in Colorado and people will get confused.
As to the first point, some people are thinking that the real aim of this group is to get the reservoir drained and the dam taken down. Whatever, it certainly is not the only reservoir refered to as a lake; Lake Mead for instance. The second point is also unconvincing. I live here in Oregon where we have about 5 Eagle Creeks. Should we round up all the water bodies in the USA with matching names and rename them? People won't get confused.
The Arizona board of Geographic Names doesn't seem moved either and isn't planning to change anything.
Besides, the lake is named after John Westley Powell, who originally named Glen Canyon in the first place.
Hat tip to the GITC America GIS Monitor newsletter.