One effective method of controlling the flow of plastic waste and debris is to capture it from rivers and canals before it can end up at sea. A bubble curtain is the solution for this problem. 

A bubble curtain is a non-invasive solution to stop plastic from entering the oceans. Ships and fish can pass through the air bubbles, but plastics will be stopped. The bubble screen is created by a specially designed air tube which is placed diagonally on the bed of the canal or river. It brings waste to the surface, channels the plastic onto the banks where it can be extracted.

The bubble barrier is generated using compressed air passing through tubes that are placed at the bottom of the canal. These tubes are connected with a compressor which is powered by renewable solar energy. Further, aeration in the canal will increase dissolved oxygen levels in the wastewater/stormwater leading to an overall improvement in the water quality.

https://www.dw.com/en/a-bubble-barrier-stopping-plastic-waste-in-rivers/av-52445644