The main river of the country is Chao Phraya, 365 km long and with a drainage basin area of 160.000 square kilometers.

An excerpt from the article 31 facts about Thailand

Chao Phraya flows from north to south through the center of the country and flows into the Gulf of Thailand. The river delta forms numerous branches and is 200 km long and 100 km wide. The Mekong, the largest river in Southeast Asia, flows along the eastern border of Thailand.

There are many lakes in Thailand, mainly on the Korat Plain. The largest natural lake is Songkhla, with an area of 1040 square kilometers, located on the Malay Peninsula.