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Updated: Jun 3, 2020

Watersheds are an area of land that drains all water to the same place. All water in a watershed drains into the same body of water - a reservoir, bay, or the ocean. When it rains (or snow melts), the water travels downhill across the ground to gather in a stream or creek. It can also soak into the ground where it will eventually seep into a stream, river, or other waterbody. The streams flow down to rivers, and the rivers dump into the outflow points (like the ocean).

If it rains in an urban area with asphalt and cement making up sidewalks, roads, and neighborhoods, the rain cannot soak into the dirt. Instead, the rain quickly runs across these hard surfaces, and as it moves downhill, it gets drained into storm drains. The storm drains then dump the water into the nearest waterbody. Sometimes, you will notice these storm drains have warnings stenciled near them to remind people that only rain should go down the storm drains.

The water that drains here goes straight into a major waterbody, like a lake or ocean, without being treated, or cleaned. This is why it is important that no one dumps anything else down the drain.

While storm drains are great for draining the city, they also gather all the pollutants that are sitting on the cement and asphalt. These pollutants multiply as each storm drain adds water to the flow. Once this water reaches the ocean, the water can be dangerous to animals and humans.

Some examples of pollutants are:

  • Oil leaked from cars

  • Litter (food wrappers, plastic cups, straws, etc)

  • Cigarette butts

  • Dog poop

  • Herbicides, pesticides, or fertilizer that gets washed away

  • Debris from construction; and sediment (dirt)

  • Yard waste (like leaves that were never racked up)

You might think, "Leaves are natural, how can they be bad for the water?"

  • Well, when leaves fall from trees in nature they decompose on the forest floor, which returns the nutrients to the soil. But in cities, they get swept across concrete into storm drains, and large amounts get deposited in one location (like the outlet of the ocean). This increases nutrients in the water, which is bad for the aquatic creatures. Increased nutrients feed algae, and the algae increases in number. After the algae "blooms" for a while it will die, and decrease the oxygen in the water as it decomposes. Fish (and other aquatic plants and animals) need oxygen, and will start to die.

  • Dog poop, or sewage, that gets in the water brings with it harmful bacteria. If humans swim in the water, it could make them sick. It also depletes the oxygen in the water, killing aquatic animals. Sewage can bleach coral, and once the coral dies, all the other animals that live on the coral reef begin to disappear.

  • Sediment (or dirt) that erodes and becomes deposited in waterways can effect the environment in a couple of ways. The dirt can remain suspended (or float) in the water, which blocks sunlight from coming through. This limits photosynthesis of aquatic plants - the plants which are producing oxygen. This reduces the oxygen that the aquatic animals need to survive. The sediment can also settle on the bottom of the waterway. The bottom may have originally had gravel and rocks which created a habitat for amphibians, fish, and other animals, but those spaces between the rocks get covered in dirt. Without the same habitat, some of these animals may disappear.

The impact of pollution on the health of our waterways, and the health of humans, is important to remember. When you see one piece of trash, or a small oil leak, just remember the video (above) where one rubber ducky seems unimportant, until it meets up with all the other rubber duckies from all over the city.

Follow this video to make your own watershed, and once you make it "rain", you can see how everything washes downhill.

Three ways you can get involved in your community to protect your waterways:

  1. Host or join a clean-up event. Keeping litter from the city streets (and natural areas like beaches and parks) will make sure it doesn't get washed into the waterways.

  2. Do your best to minimize any pollution in your own yard that could get washed away with the rain.

  3. Stencil your local storm drains to remind your community not to dump anything down them. Stencils can be bought online, but sometimes they can be rented as well. In San Diego, you can contact I Love A Clean San Diego for free stencil rentals and stenciling events (619-704-2774). Make sure you contact the City or County office where you live to get permission to stencil. (Stormwater is usually under the Department of Public Works).

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