Shirley, with all due respect, I think there are still nice places to kayak in KW. I have friends who did it and loved it, and here is the quote from DisneyDarwin's trip report. NB: The guide takes them out of KW proper, quite aways away, hence getting out of the over-developed areas, I guess.
Key West. We went ashore and took the trolley tour. DW and I had done this before, but wanted to do it again as a good way to see the town and show it to DD. At about 2pm, we met our kayak guide, Leo, from Crystal Seas. He drove us north about 20 miles to Sugarloaf, where we took 2 sea kayaks out into the mangrove forests just off shore. We saw lots of birds (my wife is an avid birder), plenty of fish and a few nurse sharks. The trip was very quiet and very pretty, a great nature experience if you are in to that kind of thing. I prefer whitewater canoeing, but enjoyed weaving throught the mangroves and viewing the wildlife and scenery. Leo was a well educated guide, and a very polite and considerate guide. Be forewarned, that on a kayak trip such as this, you actually paddle yourself about. And, you may get tired or a tiny bit wet from paddle splashes. Also, it is VERY salty off shore, and you will beg for a shower afterwards. But, if this kind of trip appeals to you, and you know what you are getting into, you will really enjoy it.