The fog was so thick that Nora Beck could barely see beyond the next stretch of boardwalk.

It was just after dawn at Billy Frank Jr. Nisqually National Wildlife Refuge in Washington State, where a king tide was pushing cold gray water farther across the tidal marsh than usual.

Beck, 38, a refuge volunteer, was walking an early-morning survey route with wildlife technician Tom Okafor, 45, when she heard splashing below.

At first, it sounded like a duck beating its wings against the water.

Then came a sharp, high-pitched cry.

Beck leaned over the boardwalk rail.

A young river otter was floating beside one of the pilings.

And it was tied to it.

The four-month-old pup, later nicknamed Pebble, had a dark brown coat and a pale patch beneath its throat. One hind flipper was wrapped in nearly invisible monofilament fishing line that had become tangled around the wooden support.

Each time the pup tried to swim away, the line pulled it back.

The tide was still rising.

“That line is holding him to the piling,” Beck said, her chest-mounted body camera pointed toward the water.

The problem was immediately obvious.

The solution was not.

An overnight windstorm had churned the estuary and scattered debris across the marsh. The young otter had likely become separated from its natal holt during the storm and entered the shallow water near the boardwalk before dawn.

Somewhere along the piling, discarded fishing line had snagged and tightened into a loop.

When the pup swam through it, the line caught around the hind flipper.

Then the tide turned.

By the time Beck and Okafor found him, the mudflat beneath the boardwalk was already disappearing under incoming water.

The fog made everything worse.

The far bank had vanished completely.

There was no clear wading route, and stepping off the boardwalk into the flooded marsh would have meant moving through soft mud, submerged channels and uneven ground with almost no visibility.

Then Okafor saw another shape in the water.

An adult river otter surfaced beyond the piling.

It disappeared into the fog.

Seconds later, it surfaced again.

The rescuers believed it could be the pup’s mother.

That raised the stakes even further.

If the pup could be freed quickly and safely, a reunion might still be possible.

But if the tide rose much higher, the trapped animal could become exhausted or be pulled underwater by its own tether.

Beck and Okafor moved carefully along the rail until they were directly above the line.

The pup struggled again.

The monofilament tightened.

Fishing line is especially dangerous to wildlife because it is strong, difficult to see and capable of cutting deeply into skin as an animal fights against it.

Okafor reached toward the section wrapped around the piling.

He could not safely reach the loop around the otter’s flipper from that position, but he could reach the part anchoring the animal to the wood.

With the pup momentarily still, he cut the line at the piling.

The severed end drifted into the water.

The otter was no longer tied to the boardwalk.

But the loop remained around its hind flipper.

And the pup was too tired to simply swim away.

The team prepared a blanket.

Beck held low at the rail while Okafor unfolded it.

The plan was to support the pup’s entire body rather than grab at the injured leg.

The first attempt failed.

The frightened animal twisted away from the blanket and slipped back against the piling.

The tide pushed higher.

They waited several seconds and tried again.

This time, Okafor lowered the blanket beneath the pup while Beck helped guide its body toward the edge.

The young otter struggled briefly, then settled into the fabric.

Together, they lifted.

Within moments, Pebble was on the boardwalk.

The remaining line was left in place until the team reached the truck, where they could work on stable ground.

At the tailgate, Okafor supported the pup while Beck slowly loosened the monofilament with her fingers.

No cutting tool was allowed near the skin.

The loop finally slipped free.

Underneath was a shallow abrasion around the hind flipper, but there was no deep laceration or obvious fracture.

Pebble was transported to a licensed wildlife rehabilitation center for examination.

The injury proved relatively minor, but the pup had been stressed, chilled and separated from its family.

For the next three weeks, rehabilitators kept him in a quiet enclosure, treated the abrasion and monitored swimming, appetite and mobility.

By the time he was cleared for release, the wound had healed.

Staff returned him to the marsh near the area believed to contain his natal holt.

Rather than immediately releasing him into open water, they used a soft-release approach, allowing the pup to re-enter the habitat gradually while observers remained at a distance.

Soon after, Pebble began giving contact calls.

Then an adult otter appeared nearby.

The animal surfaced, disappeared beneath the water and returned again closer to the pup.

For the rescue team, it was the ending they had hoped for from the moment they first saw a dark shape struggling in the fog.

The incident also led refuge staff to focus more attention on discarded fishing line around popular access points.

A monofilament recycling station was later added near the trailhead to encourage visitors to dispose of fishing line safely.

One nearly invisible strand had been enough to trap a young otter as the tide climbed around him.

Removing it took minutes.

The consequences could have lasted much longer.