River Action Executive Director Kathy Wine says it's because studies have shown that between 75 and 80 per cent of the pollution in the river is some kind of plastic.
"When they've studied the content of the pollution in the river that has been the case, and so it's kind alarming, but again it's something that people can prevent. So that knowledge and that education effort is really needed now."
And it's part of a national and global effort this month called Plastic Free July.
Wine says the problem of plastic pollution will be emphasized at several summer events, including Channel Cat Talks, Floatzilla, and Taming of the Slough. Participants will be given mesh bags that can be used to pick up discarded plastic along the river.
