The waters of Moreton Bay are relatively calm, being sheltered from large swells by Moreton, Stradbroke and Bribie islands. The tidal range is moderate at in range. Moreton Bay has an average depth of , however parts of the bay are deeper than . This relatively shallow depth lets light filter through to the seafloor, allowing an array of marine plants to grow which support a diverse range of fauna. The bay itself covers and has a catchment area 14 times larger, covering . The waters of the bay are mostly blue in colour. Western parts of the bay are sometimes tinted green from algae, brown from suspended sediments or yellow-brown from humic runoff. The average annual temperature of the sea ranges from in July to in February.