Saint John Harbour is a large, deep-water natural harbour at the mouth of the Saint John River, opening into the Bay of Fundy. It is a major industrial port and urban center, characterized by a unique tidal environment where a wedge of saltwater advances and recedes beneath the fresh river water. The harbour's geography includes notable features like the Reversing Falls at The Narrows, where powerful Fundy tides dramatically affect water flow. This creates a dynamic, brackish ecosystem that supports a mix of marine and anadromous fish species. The harbour has undergone significant environmental improvements, including a major wastewater treatment project completed in 2014 that ended the routine discharge of raw sewage.