Samus Aran reclaimed the Gravity Boost power-up in Metroid Prime 2: Echoes. It helped Samus move through the water with ease and let her do a triple Space Jump underwater (it actually makes her float, but it does the same job.) It was located in Torvus Bog, at the Hydrochamber Storage Room. When Samus collected it, she had to fight the Alpha Blogg, which was the guardian of the item (presumably a trap left by the Ing to those who would steal from them).