Answer:
It depends entirely on how dangerous you want to be.
kayaking on flat water or 3- rapids is very safe as there are many safety measures in a boat to ensure that you are able to release yourself quickly and easily and when you ensure that safety measures are in place (safety boats, bank support (throw lines)).
The dangers come when you start paddling grade 4+ water and removing those safety measures such as adding seat belts to the kayak (AKA Suicide Straps) which aid with control while play boating. Ensuring that you have a good helmet (Skid Lid), buoyancy aid and thermal suit (whether it be dry suit or wetsuit), make sure that you are a competent paddler or with competent paddlers, remember that there is no shame in getting out before a rapid looking at it from the bank and choosing a good line beforehand (or in my case usually say, 'stuff that I'm walking it'!) then the danger is very low. Make sure however that you can swim then there is absolutely nothing to worry about.
It's a good laugh and really really exhilarating.