The Cha Prayao River runs up through Bangkok from the Gulf of Siam. It provides a deep channel for about fifty miles North of the city, a little past Ayuthya, the former capitol.
This picture was taken in the port area, near the docks. Here's an outbound container ship passing a nice little, typically Thai "long-tail-boat." This long tail is a ferry of sorts, shuttling people back and forth across the river.