I've done support for several local triathlons. Many outside in the Columbia river.
All I can say is, I've done support - in other words there is lots of support! All of the tris I've been involved in have several people in the water (in the river) and several watching and there to help in pools.
the only issues we've ever had, even with all of these people there "just in case" were due to hypothermia - never had another issue and never hypothermia in a pool.
You will not be alone, and you will be with people who care and support you.