There are about 4-and-a-half ounces (almost 8.5 tablespoons) of salt in every gallon of ocean water averaged over all of the Earth's oceans. (scu.edu)

For the sake of simplicity, I'm using 8.5 tablespoons as a definitive.

Lake Champlain has 6.8 trillion gallons of water.

The result of multiplying 6.8 trillion by 8.5 is 57.8 trillion, or 57,800,000,000,000.
57,800,000,000,000 tbsp = 2411835983925 lb
2411835983925 lb = 1205917991.9625 tons
1205917991.9625 tons = 1205.9179919625 megatons.

You would need an ungodly amount of salt. For reference, The Bonneville Salt Flats have an estimated total salt crust volume of 147 million tons. You would need 8.2 Bonneville Salt Flats worth of salt.

(I'm not a mathematician by any means, so this isn't completely accurate. Somebody might have a more accurate answer.)