Each year millions of people living near the ocean flock to local beaches to take part nternationaln cleanups to help fight ocean plastic pollution. Often, they do so through organizations focused not only on cleaning up the trash but also on collecting data they share with government policymakers. But like beaches inundated with plastic garbage, the government is now awash in data on that refuse and is grappling with how to navigate that sea of information to create policies to reduce marine pollution.

“Suddenly we’ve become a large repository of beach cleanup data as more people participate,” said Keith Cialino, Northeast regional coordinator of the National Oceanic and Atmospheric Administration’s (NOAA) Marine Debris Program. “But there are challenges with ensuring the quality of the data and also deciding how to use it.”

For instance, it’s difficult to vet all the data. “Data accuracy is of utmost importance,” Cialino said. To date, NOAA has collected data from thousands of volunteers monitoring 192 beaches in the United States and 58 beaches overseas.

Nonprofit groups and individuals can follow NOAA’s cleanup protocol for removing debris from beaches and submit data to the agency’s Marine Debris Map on the quantity and types of marine debris they find, where the beaches are located and whether the beach is public or privately owned.

One part of the program focuses on searching for debris from the March 11, 2011, tsunami that struck Japan and sent wreckage from the destruction across the Pacific Ocean, washing up on beaches from Hawaii to California.

NOAA began collecting marine debris data nationally in 2011 and now funds annual trash removal and prevention projects, most of which add to a growing pool of data. Last year’s NOAA marine debris removal grants totaled more than $1.1 million and were used to fund 14 projects. One was awarded to the Hawaii Wildlife Fund to facilitate the removal of about 61 tons of trash during 35 cleanups and 84 patrols along remote coastlines on the Hawaiian islands of Lanai, Kauai, Maui and Hawaii. When the group’s cleanup and tsunami debris monitoring effort on the island of Hawaii’s isolated Kamilo Point began last December, the beach was completely covered in plastic, from tiny specs of microplastic dotting the sand to lighters, plastic utensils, ropes, tires and large plastic crates – some labeled in Japanese.

Hawaii Wildlife Fund vice president Megan Lamson carefully tallied and photographed the plastic items she encountered in a 330ft (100m) transect of the shoreline. A few local volunteers and several members of the Danish nonprofit Plastic Change, meanwhile, plucked plastic trash off the rest of the beach, placing it in large orange buckets and bags that were taken to Hawaii’s trash processing plant for disposal. Fishing nets and lines were turned into electricity at a waste-to-energy plant on Oahu.

Lamson said she learned a great deal about the amount and composition of the debris she’s collected over the years. (Her group reports its cleanup data to NOAA.) “To date, Hawaii Wildlife Fund and volunteers have removed over 214 tons of marine debris from the shores of Hawaii Island, and 248 tons if you include Maui, Midway and the French Frigate Shoals,” said Lamson. “Of this figure, we estimate that 41 percent by weight are derelict fishing line and nets. In fact, data from our 100m shoreline surveys at Kamilo Point indicate that net and line fragments are the second-most common item larger than 2.5mm that we collect, and the top item are miscellaneous plastic fragments [from consumer products].”

Mark Manuel, NOAA’s marine debris regional coordinator for the Pacific Islands, said such data has a high value in establishing a scientific understanding of ocean pollution.

“Shoreline monitoring data helps us to understand the problem – the types and abundances of marine debris, and how does that change over space and time – to identify the sources of debris and how best to stop it, and assess the effectiveness of existing prevention efforts,” he said. “We want to better understand the sources and causes of differences in debris present in the coastal environment, guide marine debris policy development and provide data that can be used in education and outreach efforts.”

Manuel said NOAA is currently working on a few peer-reviewed papers related to marine debris monitoring in the Pacific. He said his agency is also working with the Ocean Conservancy and Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) to assess ocean trash on American shores based on data collected by the three partners. Results of this analysis, which began in September 2015, are pending. The nonprofit Ocean Conservancy runs its own international cleanup program and its volunteers use a smartphone app to collect cleanup data, which is uploaded to a map similar to NOAA’s.

It’s not possible for NOAA to train every citizen science volunteer to ensure the highest quality data, Manuel acknowledged. But he said NOAA is doing a good job of remotely training its volunteers by quizzing them, providing video tutorials and requiring a post-collection review of survey data to check for errors. Indeed, an April 2017 study found that with the right preparation citizen scientists are just as capable of collecting data as trained scientists.

Sarah Kollar, project and outreach specialist of Ocean Conservancy’s Trash Free Seas Program, said one drawback to citizen science data is that it’s not always known where and when volunteers will agree to participate “Data can be patchy across years and geographies depending on the number of volunteers who participate in any given cleanup,” she said. “But we have found that the data often align with those collected through more rigorous studies. And the beauty of the International Coastal Cleanup is that we amass a large quantity of data in a short amount of time.”

The Ocean Conservancy publishes an annual report summarizing the number of beach cleanup volunteers, distance covered, the weight of collected debris and the number and types of items collected for any given cleanup. The data is also available in an online database.

Such citizen science efforts have shed much light on ocean pollution, but it’s still not clear what tangible effects the data will have on ocean policy, according to Cialino. He said that figuring out how best to analyze marine debris data is part of NOAA’s 2016–20 strategic plan. At the very least, it seems these cleanups have been effective in educating people about ocean pollution as the number of volunteers involved in beach cleanups and surveys continues to grow.

“It’s sad seeing so much trash out here, week after week,” said Nohea Kaawa, a Hawaii Wildlife Fund volunteer and Hawaii native. “But I keep at it because I hope people see the data we’re collecting and realize their actions are affecting the one home we all share – the Earth. Maybe that will change things for the better.”