| Pathein River ပုသိမ်မြစ် | |
| Name Other: | Ngawun River ငဝန်းမြစ် |
| Subdivision Type1: | Country |
| Subdivision Name1: |  Myanmar |
| Subdivision Type2: | Region |
| Cities: | Lemyethna, Ngathaingchaung, Thabaung, Pathein, Ngapudaw, Hainggyi Island |
| Length: | 183.5km (114miles) |
| Source1 Location: | Irrawaddy River near Hinthada |
| Source1 Elevation: | 30feet |
| Mouth Location: | Andaman Sea |
| Mouth Elevation: | 0feet |
The Pathein River (my|ပုသိမ်မြစ်), formerly called the Bassein River, is the westernmost distributary of the Irrawaddy river in the Irrawaddy delta of Myanmar flowing through Ayeyarwady Region.[1] The river is also interchangeably known as the Ngawun River (my|ငဝန်းမြစ်).[2]
Seafaring vessels are able to travel about 75miles inland up the Pathein River to the city of Pathein.[3] As far south as Thabaung Township, about 20 miles north of Pathein, the river becomes prone to seasonal flooding in a flood plain environment.[4]
The river also provides fresh water to the city of Pathein through a treatment plant in the village of Mayanchaung.[5]
The river diverges from the Ayeyarwady in southeastern Ingapu Township, close to the city of Hinthada.[6] The Pathein river is part of the tide-dominated Irrawaddy delta system and has several distributaries of its own.[1] The overall Pathein distributary system carries less than 10% of the Ayeyarwady River's total discharge volume.[7] It flows southwards and empties into the Andaman Sea next to Hainggyi Island.[8]
The mouth of the Pathein River is home to nesting beaches for five species of marine turtles, including the rare Hawksbill sea turtle and Leatherback sea turtle species.[9] Thameehla Island at the mouth of the Pathein River is known to be a major nesting ground for Green sea turtle and is the location of a conservation effort by the Department of Fisheries.[10]