According to Surfrider Foundation you can maintain healthy beaches and waterways if you do your part, simple things like picking up after yourself and your pet. Treat the beaches as you would your own backyard and driveway, by using trash bags to dispose of litter and debris. Even using fertilizers will impair the health of the oceans. Fertilizers leech into the water table, and make their way to the ocean. Hazardous materials, paints, medicines, chemicals that are not biodegradable should be disposed carefully. Contact your city's disposal facility for details.
Recreational boaters need to be especially careful as they move from one water source to another to wash off the debris and de-contaminate their boats before moving on to another area. There are brochures that identify species that hitchhike in your area and give instructions on how to contain them.
Do read and follow instructions.
Sometimes, we are so eager to improve our environment, that we introduce non-native species that kill off other species right in our front yard, beautiful plants that become invasive, or worse, harbor parassites that kill native flora. Entire forests of Port Orford Cedar were destroyed this way. The native Port Orford Cedar is a strong wood, impervious to water and makes an excellent building material. It is slowly disappearing in our forests.