The Tha Chin river (Thai: แม่น้ำท่าจีน, RTGS: Maenam Tha Chin, pronounced [mɛ̂ːnáːm tʰâː tɕiːn]) is a distributary of the Chao Phraya river, Thailand. It splits near the province of Chainat and then flows westerly from the Chao Phraya through the central plains, until it mouths into the Gulf of Thailand at the province of Samut Sakhon.
The Tha Chin river has many regional names. After it splits from Chao Phraya river at Chainat, it's called Makham Thao River; while passing Suphan Buri it is the Suphan River; while passing Nakhon Pathom it becomes the Nakhon Chai Si river. Only near its mouth at Samut Sakhon does it become the Tha Chin River, named after the old name of Samut Sakhon. However, for purposes of discussing the river in its entirety, the name Tha Chin is the conventional choice in most scientific documents.
Tributaries of the Tha Chin include the Kra Sieo, Yang, Tawip, Chorakhe Sam, Bang Len and Chin Si Rivers.