- [Participant] Get ready.

It's gonna get exciting.

(equipment beeping) Fishy, fishy!

Oh, I saw one!

(fish flopping) - [Narrator] Sometimes, to understand what's happening in a stream, scientists have to go fishing.

- [Participant] There it is!

- Yeah, I see it.

In your net!

- Woo!

- Sweet!

- Electrofishing is temporarily stunning the fish in the water, and then snatching 'em up as fast as you can in the net.

- [Participant] Yep, it's right here, right here!

Fish in your net.

Oh, outta your net!

Going down!

- [Participant] Oh no!

- [Participant] It jumped right in your net and then.

Jumped out!

- [Participant] The fish are doing their best to hide from us.

Oh, there it is!

Under here!

- [Participant] Next time.

- [Narrator] The fish are pretty crafty at avoiding the nets, but most will eventually get scooped up.

- [Participant] Little fish!

- [Narrator] They'll help these scientists understand how streams changed, following the most extreme fire event in Oregon's recent history.

(equipment beeping) - I remember it very distinctly, Labor Day 2020, COVID.

Everything was closed, we were in the river, that day was quite hot.

(music) It was a glorious day until it wasn't.

- [Operator] 911, what is your emergency?

- [Resident] We need help in Gates, there's a fire coming up in the neighborhood!

(fire crackling) It's huge!

Oh my God!

- [Narrator] That day, a massive windstorm moved across the Pacific Northwest, fueling more than 20 fires.

They would eventually burn more than a million acres.

When the fires were finally out, nearly a dozen people were dead, and thousands of homes and businesses were destroyed.

(music) The landscape and rivers, the sources of drinking water for millions of Oregonians changed significantly.

- [Ashley] We knew it was bad, and we knew that it needed to be studied.

- [Narrator] The team of biologists and ecologists sprung into action.

- [Ecologist] Be careful on that rock.

- [Narrator] Searching for streams that had burned at varying severities across tree plantations, older natural forests, areas where the burned trees were logged after the fire.

(logs clattering) And some unburned streams to serve as a baseline.

- This study is unique in that we have 30 streams across three big mega fires in Western Oregon.

- [Crew] I just gotta measure the depth.

- [Narrator] Every summer since the fires, the crews have tested water quality.

- [Crew] 260.

- [Narrator] And how the animals and the streams have fared.

(river bubbling) Cedar Creek burned in the Beachie Creek Fire.

What was once a shady creek is now exposed to the heat of the sun for much of the day.

(equipment beeping) - [Allison] Yep, yep, yep yep, yep, yep!

- [Crew] There it is right there!

- [Allison] I think that was a rainbow trout!

- [Crew] Nice!

- [Narrator] Many of these species depend on good water quality and cold water to thrive.

And after five years of counts, the team has started seeing some trends- - [Crew] 140... - [Allison] Despite stream temperatures getting really warm in these systems after the fire, the fish populations are remaining just as high or higher than the unburned sites are.

- [Narrator] The streams are warmer, but more sun means more algae, which feeds the food web.

Also, without trees and vegetation sucking up water on the surrounding hillsides, there's more left for the rivers.

(river bubbling) - [Brooke] With the extra rains that are coming straight down and into the stream with that runoff, you're getting additional fringe habitats along the streams.

(tools shuffling) - [Narrator] But while the fish have gotten the post-fire bump, the story isn't as clear for amphibians.

- [Allison] 3, 2, 1, out!

(water trickling) - [Narrator] Streams in the west Cascades are home to coastal giant salamanders and tailed frogs.

- [Crew] Going down.

- [Allison] Sallie?

- Oh, there it is!

- - [Narrator] The sallies are tough to catch.

- [Crew] Yeah, it's gone.

- [Allison] They're potentially the squirmiest.

- [Crew] It's waving!

- [Allison] Hello!

- [Crew] I'm just pressing his head in.

- [Crew] Oh no!

- [Allison] Oh no, no, no, no, no!

Oh no!

- - [Crew] Okay, I got three of them.

- [Crew] Okay, there's a young one here by your feet.

- [Allison] Oh, we got 'em all.

- [Narrator] Frog and tadpole numbers in particular have dropped in some streams, but the preliminary data are showing fires aren't the cause.

Instead, the declines happened in areas where logging crews harvested burned trees most heavily after the fires.

For the longest time, stream ecosystems were thought to suffer because of wildfire.

But in the five years since the Labor Day Fires, these scientists are seeing signs that they're actually thriving.

- [Brooke] Everything we thought we knew about fire, we've kind of turned it on its head here on the west side of Oregon.

- [Narrator] And the research shows that the tragedy of the Labor Day Fires has turned into an opportunity.

(river gurgling) A chance to figure out the best way to manage our forests after wildfire, to protect our streams and all the life they contain.

- [Crew] So cute!

- [Allison] The reality is that wildfires are increasing on the landscape in severity and size.

And so, in terms of understanding how we manage our forests and these ecosystems, we need to know what's happening 'cause we're really just kind of at the start of what we're gonna begin to see in the future.

(river bubbling)