New York State Police say they discovered Mara's body in the St. Lawrence River in Cape Vincent, New York on Sunday just after 8 a.m.
A preliminary investigation suggests Mara drowned while swimming.
Police say her body showed no signs of foul play and was taken to the Jefferson County Medical Examiner's Office to determine an official cause of death.
Mara was born in Syracuse, New York in 1960.
She went on to appear in many popular shows including 'ER,' 'Law & Order,' 'Shameless' and 'Ray Donovan.'
An investigation into her death is ongoing.