Water hops are a technique which can be used to navigate through water faster than usual. It is performed by repeatedly jumping as Jak lands back in the water to preserve speed. While normally slower than fast swimming, with blue eco it is a lot faster.
Water hops can be performed in Jak and Daxter: The Precursor Legacy. It remains to be confirmed whether or not they can be performed in Jak II: Renegade and Jak 3 (though they will not have use cases due to the lack of blue eco in these games).
It is not currently known how or by whom this technique was discovered.