The Chao Phraya River overflowed into parts of Bangkok and Samut Prakan province on Monday morning during high tide.
Local authorities reported pavement-deep flooding in Bangkok's Bangkok Noi, Taling Chan, Bang Khunthian and Nong Chok districts and Samut Prakan's Muang district, slowing traffic through those areas.
Traffic in Khlong Toey district also slowed as part of Ratchadaphisek Road was flooded. Another section of the same road in Yanawa district near the Chao Phraya was also flooded, forcing motorists to slow down.
The Hydrographic Department of the navy reported that Chao Phraya River level peaked in front of the Royal Thai Navy headquarters at 2.16 metres above mean sea level at 9.55am. It predicted the next peak at 2.23 metres above the mean sea level at 11.26am on Tuesday.
The Bangkok Metropolitan Administration said that discharges from the Chao Phraya dam upstream had nothing to do with the flooding.
Meanwhile, the Department of Disaster Prevention and Mitigation reported that flooding remained in parts of Phatthalung, Nakhon Si Thammarat, Surat Thani, Nong Bua Lam Phu, Maha Sarakham, Ubon Ratchathani, Nakhon Ratchasima, Lop Buri, Suphan Buri, Ang Thong, Ayutthaya, Pathum Thani and Nakhon Pathom provinces.