Earlier this month, I was scrolling through my Twitter feed when I saw something quite surprising: "Amazing day snorkel surveying Sausal Creek, #Oakland! So many fish!" wrote Matt Cover, a freshwater ecologist and Oakland resident, along with video of him swimming through Sausal Creek.

The creek, which is in East Oakland, runs from just below Highway 13 in the Oakland Hills all the way down to International Boulevard in the Fruitvale District. Cover was snorkeling in the portion of Sausal Creek that runs adjacent to Dimond Park doing an annual survey of the fish population in the creek. He said he saw 98 wild rainbow trout that day, most of which were less than 4 inches long.

I was looking at Cover's video in awe. It looked like he was deep in the wilderness when he was really in the middle of one of California's most populated cities. And then I thought, "I should do this."

When I told people that I was going to snorkel in Oakland, they expressed either confusion or concern. They thought that I'd have to drive up to the Yuba River to go snorkeling, not just down MacArthur Boulevard. Heck, some people said they didn't think it was safe to get into the water anywhere in the San Francisco Bay watershed, let alone use it to do a recreational activity usually reserved for Hawaiian vacations. A few remembered growing up in East Oakland and playing in that creek as children.

I learned the organization Friends of Sausal Creek (FOSC) has been leading efforts to clean up and restore the creek since the mid-90s. So if Sausal Creek was good enough for the rainbow trout to swim in, it was good enough for me.

Cover usually wears a dry suit while snorkeling to make sure he is protected from contaminants, but that's just because he's typically in the water for one to two hours at a time and does it more frequently than the average person.

"You're not going to ingest anything through the water in the amounts that you have to worry about," Rob Leidy, a board member of FOSC and ecologist with the San Francisco office of the Environmental Protection Agency, told me. He said he still wouldn't snorkel in the creek without a dry suit, but when I pushed him on the idea of doing it just once in swimming trunks, a top and shoes, he said I'd probably be fine.

And that was enough assurance for me.

When I pulled up to Dimond Park the day of the mission, I was a bit nervous. I got a few weird looks walking into the park carrying a snorkel, a GoPro, boat shoes with holes in them, and a towel with a fish on it that looked like a "Finding Nemo" knock off. I was wearing a long-sleeve sweatshirt with the words "Marine Biological Laboratory" on it, likely to compensate for my lack of experience with snorkeling in an urban stream, or anywhere.

Oh yeah, I forgot to mention: This was my first time snorkeling. Ever. I'd played with snorkels as a kid and even threw one on and got into the shallow end of a pool, but never the real deal. Until now.

As I sat on a rock in the park and changed into my boat shoes, I thought, "Well, if this goes terribly, at least I got two hours off of work to go play in a creek." The childhood version of me that used to jump from rock-to-rock in creeks in the Washington, D.C. area was proud of the 33-year-old version of me that was getting paid to do basically the same thing.

There were well-worn paths down from the park to the creek. While walking on one of them, I noticed that there was a tent on the bank opposite the park. I hoped that if there were people living in it, they weren't using the creek to relieve themselves, or at least hadn't done so recently. I know I probably would if I had a creekfront property.

Cover sent me directions to the pools where there would likely be fish to see, so I headed over to the first one, which was behind a pair of apartment buildings, downstream from where we entered the creek. I wondered if there was anyone who was looking out of their window, going about their day, only to see a black dude with a snorkel on his face swimming around in what serves as their backyard.

It wasn't an issue for me to walk in the creek, which ranged in depth from a few inches deep to a few feet deep. I didn't care about the shoes I was wearing and the temperature of the water didn't register quite yet. There was a bit of a trudge to get to the pool, but once I got there, I swiftly lowered myself into it and was immediately reminded of how cold the water is here in Northern California.

It wasn't as freezing as coastal water can get, but it was still disorienting enough that I only stayed underwater for a few seconds. That was long enough to make the water so cloudy that once I summoned the nerve to dive back into the pool, I could barely see inches in front of me, let alone spot a fish. I also fogged up my goggles for the first of several times, which reminded me of how much of a newbie I was.

I felt defeated after that first failed dive, but I saw fish in a much smaller pool on our way back upstream, and that felt like a good time to try again. That time, I was successful. I saw a few of the smaller fish Cover was talking about in the tweet that kicked off this whole adventure, stayed in the water for more than a few seconds, and didn't fog up my goggles. I didn't know until later that I'd also caught the fish on the GoPro.

I got several side eyes from people in the park as I emerged from the creek looking like the Creature from the Black Lagoon. I tried my best to ignore them and walk upstream to the next pool.

"Good luck fishing!" joked a guy who was walking his dog. I told him I wasn't fishing, since that's illegal to do in the creek because the fish populations there, while recovering, are low.

When Cover was talking about his snorkel survey on Twitter, he said the number of fish he saw this year (around 98) was a high-water mark in the five years that he's been doing the surveys. The previous high was nine.

"The fish population in Sausal Creek is pretty small," Leidy explained. "There are only a limited number of big pools where fish can survive through the summer, and so there are not a lot of reproducing fish.... We know that if people are effectively pulling out three, four or five of those big spawning fish it can have a real effect on the population and sort of reduce it."

When I got to the next pool, I noticed that it was larger and deeper than the first two, Even though it was still shallow (only about 2 feet down at the deepest point). I'm a great swimmer, but the fear of drowning in a creek (and surely getting dunked on for doing so by my friends and family after they sufficiently grieved me) crept into my head.

But I was glad I didn't let that fear stop me. Once I was down there, I could see several feet ahead of me and there were fish racing around and in front of me. For the moments I was underwater, it almost felt like I was snorkeling on vacation in the tropics, not at work in Oakland.

While the first three pools all looked and felt like safe places to get into the water, the fourth, last and largest pool was more like what my friends likely pictured when they expressed concern over my urban expedition. The pool of water, about 15-feet wide, 20-feet long, and 3- or 4-feet deep at the low point, sat at the mouth of a large stormwater drain.

If it were a drier year, I might not have gone into the water in that pool, but there was likely enough water from our wet rainy season to flush out anything gross. The water was less clear than the other three pools, but you could still see nearly to the bottom and glimpse fish swimming around from the bank, so I was game.

That was a questionable call. I should have guessed from the can of Modelo that was drifting along the edge of the pool that it might taste a bit like hops, but I took the plunge anyway.

The traces of water that got into my mouth indeed tasted a bit funky, like stale keg beer. I was worried that I'd ingested some contaminant for a couple of hours after I was done.

Regardless, I think it was still worth it (though I'm holding out to see if the creek water makes me sick). When I got down to where the fish were, I noticed they were adult rainbow trout. They were all between 6 and 12 inches long and were swimming in circles, some chasing others around. I saw about 10 to 15 fish while underwater for the last time.

Despite internalizing the concerns of my friends and family, moving through my own fear, and that gross frothy taste the last pool left in my mouth, I had a ton of fun and, if I had a dry suit, I'd do it several more times. I know environmentalists who think of wilderness as far outside the reaches of bustling cities, but that's not always the case, especially not in the Bay Area.

Sausal Creek in Oakland is proof.

Drew Costley is an SFGATE editorial assistant. Email: drew.costley@sfgate.com | Twitter: @drewcostley