[TakerofVita]

I would think that the fact that it is fresh water vs. salt water wouldn't impact sea level on the basis of changing density.

Take two situations:

1. A mass of sea water is replaced by the same mass of fresh water. Sea levels/volume would increase as the average density would be lowered. (this is not the case)

2. A volume of fresh water is added to the ocean. Then V_total = V_ocean + V_freshwater.

[adrianN]

Volume is not necessarily conserved when mixing liquids. Check the Science Guy:

https://www.youtube.com/watch?v=84k206qaVRU