Si Yaek Maha Nak (Thai: สี่แยกมหานาค, pronounced [sìː jɛ̂ːk mā.hǎː nâːk]) is a sub-district (khwaeng) of Dusit district, Bangkok.

The canal has a starting point at the Khlong Rop Krung (คลองรอบกรุง; lit: around the city canal), part of the old city moat, from Saphan Mahat Thai Uthit (Mahat Thai Uthit bridge) near Ratchadamnoen avenue and then Mahakan fort passes through to the east.

It was the centre of travel and trade by boat and connected to Chachoengsao province by Khlong Saen Saep.

[2] There's an incredible story behind this area's naming of "Si Yak Maha Nak", it is due to Mae Nak Phra Khanong, Thai female ghost, and was well known as being haunted by her inflating her body to a gigantic size here.

In addition, it's also adjacent to Bobae, wholesale and retail cheap clothes market located in Pom Prap Sattru Phai district.