Ice melts faster in fresh water than in salt water. The higher the salt content, the slower the ice melts.
Ice melts as it reaches 32 degrees Fahrenheit. When it's in the water, a heat transfer occurs, cooling the water but warming the ice. However, fresh water cannot cool to a temperature below 0 degrees and in most cases, doesn't get that cold. Salt water, on the other hand, has a lower specific heat, meaning it can cool much lower. Since the fresh water holds more heat, it's easier to draw heat from the ice cube and melt it.