Why is the water so cold in California?

I'm not from the area, but I visited people a couple years ago near Monterey. I'm from the East Coast and the Gulf, so when I got there the first thing I said was "LETS GO SWIMMING!"... and was pretty much just laughed at and told that you can't go swimming in the waters there without a wet... show more I'm not from the area, but I visited people a couple years ago near Monterey.

I'm from the East Coast and the Gulf, so when I got there the first thing I said was "LETS GO SWIMMING!"... and was pretty much just laughed at and told that you can't go swimming in the waters there without a wet suit, even though it was the middle of summer.

Is it because of the Trenches? Or are there other reasons why the water is so cold?
Update: I meant I am from the East Coast... not just South Florida. VA, NC, and GA.

I've lived alot of places, just not California. I'm actually pretty ignorant about California in general.
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