How big does a lake have to be in order to have seagulls?

You can see seagulls in cities and dumps, away from any sea water. They live wherever they can get food, that's all.

It doesn't so much have to do with size as -what I would suspect- proximity to existing seagull populations. You see seagulls over parking lots (certainly not a large "lake") an hour and a half outside of Chicago.

Yea our walmart has seagulls. (not for sale :D)

I live about 400 miles from the ocean, but every spring the local college and high school football fields are covered with seagulls. I later learned that they come to the fields to mate and then fly to an island in a lake about 30 miles away to lay eggs. The lake is probably 5 square miles.

size doesn't matter

From what I understand, they don’t need water. Some species of seagulls prefer water and some don’t. Maybe Lake Tahoe doesn’t offer the kinds of food they like or are otherwise unihabitable.

We have seagulls in the Walmart parking lot in Ohio . . .