As an individual you can make a big difference just by changing a few habits. The most important habit to change is to try to stop buying new plastic in any form, where possible. This can be really difficult so start with the easy ones and work your way along to the tougher changes. Maybe they will change for you as there is a lot of help coming along from the manufacturers and packaging companies. We need to choose these new products, if affordable, so that more change happens more quickly.
Another great way to help combat the plastic issue is to carry out litter-picks, either on your own (which is nice and peaceful) or in a big group which can make a massive difference really quickly. There may be regular litter-picks already organised in your local area. If not, why not start something! Beach cleans are especially rewarding but stopping the plastic and other litter getting into watercourses in the first case is far more effective.
River cleans are only carried out by experts with safety equipment so don’t put yourself in danger whilst litter-picking. Avoid roadside litter-picking for the same reason.