The old man's ashes were sent into the river, accompanied by mountains and rivers. As long as the deceased is angry, there is no taboo to scatter the ashes into rivers, lakes and seas. The only thing to pay attention to is to shade the sun when there is sun, and not to expose the ashes to the sun for a long time.
After the river burial, you can also worship. Those who have religious beliefs can put coffins in temples or at home and worship at festivals.
You can also leave some ashes buried in the river. Of course, you can also choose the clothes of the deceased to make a cenotaph, leaving a thought for the living.