Walking the Watershed

Walking the Watershed

Explorer Shannon Switzer treks one of San Diego’s longest rivers, starting in the mountains and ending in the ocean, and documents the pollutants affecting its health.


4 - 12+


Biology, Ecology, Earth Science, Oceanography, Experiential Learning

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Shannon Switzer is a water conservationist, photojournalist, and National Geographic Young Explorer Grantee.

The ocean along the coastline of San Diego, California, is my first home. When I was a little girl, I would sail to Catalina Island every summer with my dad, and swim through the kelp forests—right alongside bright orange garibaldi and playful sea lions.

More recently, I started getting sick and developing ear infections after being in the ocean. My friends were also getting sick, and two almost died after contracting life-threatening bacterial infections.

I wanted to better understand why this was happening. So I decided to explore and photograph the rivers and streams that drain into our ocean, to understand the connection between what pollutes the water on land and how it affects the coastline. A large part of my project involved trekking the San Dieguito River, from its headwaters in the mountains right down to the ocean. Join me on this 145-kilometer (90-mile) journey!

February 22, 2011

After weeks of preparation, I finally set out on the trek with my hiking partner, Read, this morning. It was cool and clear when we drove inland from our homes near the coast.

When we reached our starting point at the foot of Volcan Mountain by early afternoon, the air was fresh and crisp, but the sky was filled with gray clouds. It has been a wet winter for San Diego—we’ve already gotten 20 centimeters (8 inches) of rain, when our average annual total is about 25 centimeters (10 inches). This explains why there was almost a meter (2 feet) of snow in Julian, an old gold-mining town near Volcan Mountain.

Before we could start making our way down the San Dieguito watershed, we had to get to the top of the 1,783-meter (5,850-foot) peak, where the river begins. As Read and I climbed up, boots crunching on snow, the trees changed from oaks and manzanitas, with their signature shiny bark, to a variety of evergreens. The air grew colder as we reached the top, where the view was stunning. When we looked east, we could see the Anza-Borrego Desert stretching out for kilometers until it hit the San Felipe mountain range, and the skies were blue and clear. Spinning 180 degrees, we stared west over thick gray clouds, white snow, and muted colors. The clouds led our eyes to a thin line of ocean sparkling on the horizon, calling us to it.

The sweat I worked up during the ascent had dried and left me feeling frigid. We descended and connected to a trail that meandered through pastureland dusted with snow. We pitched our tents in the middle of a field at the top of a hill, carefully avoiding cow patties that littered the ground, and fell asleep to the sound of cows mooing at the stars.

February 25, 2011

Today was our toughest day so far. We had nothing resembling a trail to follow and were left with only thick stands of poison oak to navigate and rushing rapids to wade across. Last night Read and I hiked through Boden Canyon, where we saw scars from past mining operations cutting into the reddish-brown canyon walls. The crumbling walls made the scars look as though they were bleeding. This morning, we took down our tents as a lone coyote watched from the distance, and continued west, walking deeper into the canyon.

As we progressed, the walls grew steeper and the vegetation denser, leaving us no way forward. We bushwhacked on one side of the river as long as possible, then crossed to the other side, battling thick stands of a bamboo-like plant known as Arundo. Arundo is an invasive species that chokes waterways in San Diego, causes erosion, and fuels wildfires.

I was running out of drinking water, and we couldn’t drink the river water because of all the bacteria from cow manure and chemicals from agriculture. We’d been warned that even filtering or boiling river water would not guarantee it safe to drink. We had placed water at strategic locations before beginning the trek, but still had kilometers to go before we reached our next stash.

I focused on the terrain ahead. After we’d gotten through the narrowest part of the canyon, the walls sloped at a less severe angle and we were able to pick a higher line to walk. This posed a new challenge: Water that ran down the canyon walls and fed the main river had cut deep ravines, which we were now dipping into—and climbing back out of—every few hundred meters. After several hours of this, my mouth felt like cotton. All I could think about was our “safe” water, hopefully still waiting for us a few kilometers ahead near a strawberry farm, the first of many farms we’d be crossing once we got out of the canyon.

March 1, 2011

We knew we were getting closer to urban development when we saw the lights of North County Fair Mall, a large complex surrounded by a massive parking lot. After days of walking through woods, pastureland, shrubs, vines, brush, boulders, and farmland, it was strange to see these tall buildings. On the horizon to the west, we could see what looked like red and white Christmas lights strung along the edge of a house. They were the lights of cars stuck in rush-hour traffic on Interstate 15, one of the busiest freeways in California.

This morning, we woke early, while it was still dark, to finish our final and longest stretch of the trek. Read and I crossed under the freeway we’d seen from a distance as cars whizzed overhead, each one releasing oil, exhaust, and copper (from their brake pads), which all washes into the river and ocean during rainstorms like the one we had last night. Past Lake Hodges, created by a manmade dam, we walked along the old aqueduct system that used to bring water from the reservoir to inhabitants in the city. It was filled with trash of all kinds—Barbie dolls, plastic water bottles, abandoned furniture, and old car parts, just to name a few. We continued on our path, through housing developments with tidy lawns and golf courses, which require a lot of fertilizer that washes into our streams.

As soon as we hit the edge of the last golf course, I felt my first ocean breeze. We continued under Interstate 5, another busy freeway, and came upon tidal marshland. Tidal marshlands like this one are important features of the landscape because they filter out contaminants before they reach the ocean and provide a nursery for many species of fish, birds, reptiles, and insects. Wetlands like these have become a rare thing in Southern California because most of them have been filled and developed for tract housing.

Finally, we crossed Pacific Coast Highway (Highway 1) and made our way to the mouth of the San Dieguito, where it was spilling into the ocean at Del Mar’s “Dog Beach.” Pups of all shapes and sizes were playing along the sand. I couldn’t help but wonder how many of their owners were actually picking up their dog’s poop before it was swallowed by the waves. But as I watched the dogs play, tongues flapping and tails wagging while they romped in the waves, I stopped worrying and started playing too. I ran to the water and did a few cartwheels to celebrate that we had made it home.

Just like the drops of water that started as snowflakes in the mountains, Read and I trickled our way down through the land, and fell into the ocean.

Fast Fact

To Dam or Not to Dam?
We all need clean freshwater to live, and dams are one way of providing that. Dams can also be used to create electricity. However, dams severely alter the hydrology of a river. They cut off water and sediment flow downstream, stop the natural movement of fish and other river inhabitants, and limit human recreation.

American Rivers has developed solutions to many of these problems. The national organization has demolished old dams that are no longer serving a purpose, allowing rivers to return to their natural state. It has also created designs for new dams that are more river-friendly, with features like fish passages, river flow ports, and increased recreational opportunities. This creates a win-win situation for the whole community.

Fast Fact

Healthy Headwaters
Whether they come from an underground spring, snowmelt, glacial melt, wetlands, or several small creeks that come together to form one large tributary, rivers have to start somewhere. These sources are known as headwaters.

Headwaters are plentiful across the United States and help connect the landscape. They provide valuable services like controlling flooding, supplying freshwater, and creating habitat and food for many species of animals.

Finding a rivers source can be challenging. Next time you go on a hike, turn it into an adventure and see if you can find the headwaters of one of your local rivers or streams. The Environmental Protection Agency's Surf Your Watershed application can help you get started.

Fast Fact

Plant Invaders
Some plant species end up where they shouldnt beor at least where they never existed before people put them there. We call these invasives, and they can have negative effects on the health of an ecosystem.

Some invasives thrive in their new environment so much that they push out native plants that provide important resources for a wide range of critters. When these negative effects become apparent, people often try to get rid of them and restore the habitat to a healthier state. This is the job of a restoration scientist.

Media Credits

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Shannon Switzer
Jeannie Evers, Emdash Editing, Emdash Editing
National Geographic Society
Last Updated

November 27, 2023

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