SAN DIEGO — Three years ago, Dimitri Deheyn noticed intensely blue stringy shapes as he examined jellyfish samples through a microscope in his marine biology lab at the Scripps Institution of Oceanography at the University of California, San Diego.

He assumed his lens was dirty, so he wiped it off with a special cloth. Then he tried taking it apart and airbrushing the optics. But the particles kept showing up.

At first, Dr. Deheyn thought the culprit might be microplastics, tiny plastic bits that have invaded the oceans in the past decade. But a quick literature search revealed that the stringy shapes, each about a fifth as wide as a strand of hair, were actually microfibers from fabric. He wondered if they came from his students’ clothing, or the aquarium where the jellyfish was kept, or the freshwater used to wash down the equipment. But after he collected seawater samples from off Scripps’ research pier, it became clear that they had come in with the jellyfish from the ocean.

Dr. Deheyn’s microscope problem prompted him to join the growing number of scientists who are scrambling to understand the magnitude of the problem of microfibers in the environment. We shed them while running in our fancy moisture-wicking apparel, and we release a river of them when we wash our clothes. They find their way into our waterways, our drinking water, the fish we eat and even the air we breathe. One 2018 study of the distribution of plastic particles in seawater found that 91 percent were microfibers.

“They’re affecting the ecosystem in ways we’re not aware of,” Dr. Deheyn, a Belgian native raised in Rwanda, said in an animated French accent. “We don’t know if they generate cell stress, or are responsible for chronic disease, or if they can irritate the lungs.”

Dr. Deheyn started his academic career focused on studying the mysteries of bioluminescence and how changes in the light or color of aquatic animals reflected their health. Now he has made his lab a hub of microfiber research, devising novel and creative approaches to document their effects on health and marine life, which he says is drastically understudied.

“We’re trying to collect air, water and sediment samples to see where the fibers are and what’s driving them,” he said.

Dr. Deheyn has cultivated a vast network of researchers and citizen-scientists to bring him samples that provide snapshots of microfiber pollution in various locations.

“Some activist just asked me, ‘I’m going to French Polynesia, can I bring something back?’” he said.

During the French swimmer Ben LeComte’s attempt to cross the Great Pacific garbage patch in 2018, Dr. Deheyn asked researchers on the support boat to collect water and fish samples. He also works with Greenpeace, as well as the Manhattan-based Explorers Club’s Young Explorers Program, whose members brought back snow and water samples from the North Pole. (There were microfibers in them.)

Soon he hopes to get a bird’s-eye view as Robert DeLaurentis, the “Peace Pilot” who began a six-month pole-to-pole circumnavigation around the globe in November, agreed to place squares of sticky tape on his plane’s nose and wing tips to measure microfiber concentrations during 30 flight legs over cities, rain forests and deserts.

Dr. Deheyn is also working with Lenzing, an Austrian producer of cellulose fibers made from wood pulp, to test their biodegradability — part of an industry attempt to reduce the synthetic materials frequently used in soaringly popular “fast-fashions.”

Every Friday morning for this project, Holly Nelson, a college senior in Dr. Deheyn’s lab, walks onto the Scripps research pier over the sparkling Pacific and hauls up three metal baskets bobbing near the water’s surface. She pulls off long ropes of dangling kelp and collects about two dozen mesh pouches containing business card-size swatches of fabric ranging from cotton to polyester and spandex.

Back at the lab she examines them under a microscope to document the ocean’s toll on the materials, from the effects of sunlight and wave action to the variety of sea life that grows on them. She is part of a team that has spent the last year tracking how quickly the fabrics disintegrate in seawater. A second experiment looks at another set of swatches on the ocean floor 30 feet below, where they are at the mercy of abrasive sand and more microbes.

Dr. Deheyn saw the pier project as an opportunity not only to test Lenzing’s cellulose material but also to look at how other treated synthetic materials break down in real time. (Traditionally, clothing manufacturers test chemical dyes, ultraviolet protection and water-repellent agents with enzymes in a temperature-controlled closed bioreactor for a few days to a month.)

He was surprised when one polyester swatch that had been in the ocean for 200 days was still largely intact.

“If it was a tee shirt, you could still wear it today,” he said.

In the Scripps research aquarium, Dr. Deheyn is also running a parallel study in which more swatches are placed in individual containers to record how many microfibers they release. Using an instrument developed by Jessica Sandoval, an engineering student, researchers shine a black light to make them fluorescent and then use software similar to what’s used in facial recognition to capture their unique stringy shape.

Such creative approaches are welcome in a field that has struggled to accurately chronicle the spread of microfibers, said Mary Kosuth, a doctoral student in environmental chemistry at the University of Minnesota. She has developed her own microfiber data sets by studying beer and sea salt sold in grocery stores.

When scientists started studying the impact of plastics in the ocean during the last decade, they relied on nets designed to trawl for plankton, which missed the microfibers. Today, researchers are also using the “grab sample” method: They fill a jar with water and then determine the chemical makeup using spectroscopy technology that measures matter with electromagnetic radiation.

“This is something that’s growing in our collective consciousness,” Ms. Kosuth said. “We have a pretty good body of research that these particles are ubiquitous.” This year she tested a sample of her backyard snow and now forbids her two young children from catching snowflakes on their tongues.

But researchers still have a long way to go to prove that all these fibers are hurting human or animal health.

“There’s been little work done, said Chelsea Rochman, an ecologist at the University of Toronto who studies the health effects of plastics. “We know we’re exposed, but we don’t know what the consequences are, if any.”

Of particular concern are fibers, both synthetic and natural, that have been treated with chemicals during the manufacturing process or that might absorb other contaminants in the environment. There is some research suggesting that microfibers can affect crustaceans’ reproductive systems by making them lay fewer eggs or produce offspring that were stunted or died sooner than normal. In Dr. Deheyn’s lab, Alysia Daines, a visiting scholar from Aarhus University in Denmark, is testing their effects on the development of sea urchin embryos.

Amid this uncertainty, Dr. Deheyn speaks to fashion industry conferences on the need to produce fewer synthetic fabrics, and more clothing manufacturers are reaching out to him. Entrepreneurs are making washing-machine filtration systems that would catch fibers before they enter the environment, and consumers are embracing new business models, including clothing rental or resale, that could lessen the fashion industry’s impact.

“Climate change is so big that people have a hard time getting their head around it,” Dr. Deheyn said. “But the choice of what we wear and how we wash our clothes, people can grasp that concept.”