Deep water fear - kinda ruling and ruining life

I have had a couple of panic attacks in open water depite having competed in Triathalons for a few years.
What helped me to get over it was to get my head and breathing right by singing a song when I was in the water.
If you keep to the rhythm of the song going in your head you will be relaxed.
When you stop breathing or hold your breath you panic so the idea is to keep breathing. Singing or saying a poem will help you concentrate on your breathing.
100 Green Bottles was my Song ............
Hope this helps...

I'm an American who has been through (successfully through) a course of therapy for anxiety. I still have anxiety, but it is appropriate and I have tools for dealing with it properly that I did not have before therapy. That's what therapy is for; I am not necessarily suggesting you do what I did.

I did want to put to you that it is your body that is panicking (=having biological reactions suitable to dealing with an immediate physical danger), and your brain that is attempting to be a team player by making up reasons why you feel so anxious. One good workaround my therapist taught me is to imagine that the anxiety is being verbalised by an alarmed and chattering little monkey on my shoulder (a manifestation of the biological, primitive "monkey mind"). You, the functioning and thinking adult human who has better information, can tell the chattering monkey, "Thank you for alerting me to this apparent danger. I get the message. You can stand down now; I understand the situation and I am dealing with it in the best way". Or words to that effect.

A more permanent and useful tactic, that I have used myself to calm frightened people in airports, is EFT tapping. I don't believe all the woo-woo about chakras and pressure points and energies; I suspect that it works to calm down the panicky body so the mind can process the situation rationally. Whatever. It does work, and it works fast. There are plenty of free resources online if you want to explore it on your own, enough so that you don't need to buy anyone's book or seminar.

Edit: I asked around and apparently this sort of thing is more common than I expected among people who work and do sport in and on the water. (I know a lot of offshore oil rig workers, US Marines, and such.) A friend who is a decorated Marine officer said he believes it is due to the physiological effects of being in the water, and his solution was to put himself in dangerous situations in a controlled way until they no longer triggered him. But of course it was; he's a Marine.