In addition to the suggestion Coach Bob made above you might want to consider purchasing or borrowing s swim buoy for your open water swims. Besides making yourself far more visible to boaters they can also provide some support while resting in the open water rather than treading water. They are not approved flotation devices -- they won't keep your head above water but you can use them to get a bit of a rest before continuing on and others can spot you quite easily as they tend to be made of orange or yellow material (though mine is pink).
They attach about your waist and trail behind you, roughly over your feet or lower calves. You do occasionally feel them drifting across your legs but they're not really distracting.
there are several different brands out there that can be found at all the usual locations (TI store, Amazon etc)