I agree with the GP about the air pollution. I also find the Salt Lake reeks in the summer. When I would go with my dad as a kid on his business trips, the smell in the summer was really off-putting. I think it's the same problem Mexico City has. Salt Like City is in a bowl, and there's no coastal winds to blow the pollution away like the bay area has, so the pollution just lingers. I do think it's a really clean city on the ground though and Park City is so close and really amazing for Skiing / Snow Boarding. The national parks in Southern Utah are also top notch.
More specifically, it's the smell of brine shrimp decaying on the lakeshore. But it's actually not a common occurrence for the Salt Lake stink to be present in the city itself. OP was just lucky!
