Also 135.355 Emergency Flotation Device:
Basically cannot operate an aircraft with a seating capacity of 10 or more seats in any overwater operation without a life preserver or floatation device.
It essentially means if you fly over rivers and/or lake you need life jackets. Paragraph B allows Director to approve operation without use of floatation devices.
However, in many parts of Indonesia rivers are more than likely your best ditching option. I think back to Garuda 421 which ditched in the Bengawan Solo River.