Photographs of the little reptile posted on Facebook on Tuesday prompted locals to stand by the canal hoping to catch sight of the crocodile.
Residents have been warned against swimming in the canal as it may be dangerous.
Khlong Prapa runs through different parts of Bangkok such as Don Muang, Prachachuen and Tao Poon areas and also leads to the neighbouring provinces of Nonthaburi and Pathum Thani.