Definitely the undertows... watch for red flags and obey them!
Watch out for jellyfish!! Take a flashlight when walking the beach at night so you don't step on the ones that wash up. I was stung when I was swimming once... not fun!
There are some shady people down on the beach. Just use common sense and don't leave valuables out on the beach. Always lock your condo/hotel doors- even on the patios. People have climbed up several levels to steal stuff out of unsuspecting rooms on the 5th or 6th floor.
Use a heavy sunscreen... becareful of drinking in the sun. Take breaks from the saltwater and the sun. Stay hydrated.
If you want to swim you need to know that 6000.00 gallons of raw sewage were released into Mobile bay today 3/15/12 and they continue to find oil on the beaches. Maybe you should consider Florida east coast.
Look out for those blue things ,these is jellyfish,dried one ,but if you hold it long enough you can burn yourself.