The tidal spear was a long, spear-like weapon that served as Gaaki's Toa tool when she was a Toa Hagah.1 Gaaki used it to channel and focus her elemental power of water. Like the lava spear and cyclone spear, it had additional abilities, although it is unknown what they were.2
Gaaki presumably acquired the tidal spear when she became employed as one of Teridax's Toa Hagah3 (all Toa Hagah were equipped with similar spears4). When Gaaki was mutated by Roodaka into a Rahaga, the tidal spear was mutated into a small staff.5 When Roodaka reversed Gaaki's mutation, the tidal spear returned to its original form.CN Gaaki presumably continued to use the tidal spear on Spherus Magna.