It is not uncommon even for experienced pool swimmers to experience moments of panic in an open water swim, particularly in crowded conditions. USA Swimming recently published an excellent article on their website outlining strategies to tame feelings of open water panic.
A key strategy is acclimation. We have a number of short open water races on our Upcoming Events page (type “OW” in the search box). These OW swims are usually quite a bit more relaxed — and less crowded — than the swim leg of many triathlon races. The cable swims at Chris Greene Lake are a particularly good opportunity to transition from the pool to the open water.