Why is it difficult to swim underwater in the great salt lake?

I believe the answer is: because The salinity of the water is very high.

salt increase the overall mass of the water and makes the water become denser than (less strayed particle) Compared to normal salt. Objects float better on a dense surface (less strayed particle). Which mean that when you swim on the salt water, it would be hard for you to stay submerged under the water.