Axolotls are bizarre creatures.

The lake-dwelling salamanders have furry external gills, can regenerate lost limbs and tails, and often come with an eerie white skin color. Also, they are critically endangered after pollution and invasive species have threatened their tiny habitat in a lake under Mexico City.

So the last place you might expect someone to help them live more comfortably in captivity is in Bellevue. That’s where Jonathan Smith comes in.

The fifth grader has invented a device which helps his strange axolotl pet “Axy” live a happier life.

Axosafe, Smith’s company (of which he is chief executive officer) creates the device to be placed in home aquariums. The golden-colored plastic fits underneath the water filter, breaks up the flow of water to create more turbulence over a wider surface area and adds more oxygen into the water.

Axolotls, it would seem, do not like much movement in their water.

“Axy would mostly stay in the opposite corner of the filter,” Smith said. “And when it turned on, he would start swimming around in circles really fast.”

Smith, a student at Bellevue’s Open Window School, became interested in axolotls after his Fourth Grade science teacher, Randy Hollinger, brought some of the animals in as eggs from the University of Kentucky’s breeding program.

Native only to Lake Xochimilco in Mexico — which exists mainly as canals in the sprawling metropolis of Mexico City — the sensitive creatures are dying from pollution and from Asian carp and African tilapia dining on axolotl young. The “water monsters” of Mexico, once a staple of the Aztec diet, are at risk of dying out in the wild.

While nearly extinct in the wild, axolotls are a semi-common household pet and can be purchased online or from pet stores.

“We raised them and conducted an experiment on several of them,” Smith said. “We wanted to see whether they grew faster in cold or room temperature water. Room temperature was much faster.”

After the experiment, some of the students were allowed to take the animals home. Smith got Axy and a classmate got another axolotl named Marshawn.

“That must have been the catalyst that started Jonathan on his journey to Axosafe,” Hollinger said. “Regular filters and pumps provide too much water movement for the axolotls, so he became real interested in designing something to change that.”

Hollinger said the “Four Cs” of axolotl care were Clean, Cold, Calm and de-Chlorinated (“we cheat on that last one,” he said). Filters help with the clean aspect, but disrupt the calm.

Smith designed a plastic prototype in one of Open Windows’ computer labs on a modeling program called 123D and printed it out on a 3-D printer.

The first prototype didn’t quite fit Axy’s needs.

“We mailed it to the University of Kentucky to see if they could use it in their program,” Smith said. “We didn’t hear back from them all summer. Finally they emailed us back and told us how we can improve it.”

The current Axosafe model “Stream” has a grid pattern to break up the flow of water, a spillway of sorts and even a plastic cover that Smith admits is more-or-less just to make it look attractive. It snaps onto an aquarium filter. He sells them on his self-designed website for $10 each.

Smith continues to work through Open Window’s labs to design better models of the device, and said that the University of Kentucky is interested in his advancements.

“It’s really wonderful,” Hollinger said of the project and Smith’s drive. “And one of the main ingredients that helped him do that was not just his natural academic abilities — of which he definitely possesses — but also by working in an academic environment which can adjust and change and meet the needs of students.”

Open Window School is a tech-forward elementary and middle school for gifted students with magnet science programs.

Smith’s mother, Soojung Smith, said the school is able to intertwine an excellent education while still allowing students to pursue their interests.

Calley Hart, the school’s admissiones director, said the school’s environment was a fertile one for Smith’s invention.

“Within the supportive environment of like-minded peers and teachers who ‘get them’, our students feel free to explore their interests and passions.”