Water polo combines staying afloat with competing, so it is read as striving while emotions churn around you. It may reflect how much effort it takes to keep your head up and still play your part.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.