It's no surprise that bottle caps, plastic bags and other pieces of trash are washed off the streets and into our waterways every day. Some studies have shown this pollution can amount to 580,000 pieces of plastic per square kilometre in the ocean.

Plastics have a devastating impact on sea life, and according to some estimates, it's only going to get worse.

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Scientists from the CSIRO, Australia's peak science body, and Imperial College London have projected that 90% of seabirds today have plastics in their stomach, and at current rates, that number will grow to 99% by 2050.

"Finding such widespread estimates of plastic in seabirds is borne out by some of the fieldwork we’ve carried out where I’ve found nearly 200 pieces of plastic in a single seabird," Denise Hardesty from CSIRO Oceans and Atmosphere said in a statement.

Seabird species like albatrosses and penguins often mistake the brightly coloured bits of rubbish as food items, and the plastics can cause weight loss or even death.

To measure how much plastic the creatures are exposed to, scientists matched the locations of debris in the ocean with how seabird species are distributed globally, Chris Wilcox, senior research scientist at CSIRO Oceans and Atmosphere, told Mashable Australia.

Their model used ocean currents and population size along the coast globally to estimate how much plastic enters the sea. "We assume the coastline produces plastic waste in proportion to the population," Wilcox said. "You can then create a map of where plastics are expected to be."

The Great Pacific garbage patch is a notorious phenomenon, but the southern edges of Australia, South Africa and South America are the areas of greatest concern. This is where the millions of pieces of floating plastic overlap with the habitat of a significant diversity of seabird species.

Plastic fragments washing in the surf on Christmas Island in the northeastern Indian Ocean. Image: CSIRO/Britta Denise Hardesty

The project's larger research effort is aimed at addressing a whole host of problems: Where plastic goes in the ocean, how it affects ocean species from seabirds to turtles, and what an effective policy response could be.

Bottle deposit schemes, rubbish traps in storm drains and anti-littering drives are all possible solutions, Wilcox suggested. "We found in Australia, if local councils have campaigns against illegal dumping, that can make a significant impact on the amount of ocean plastics in their area."

He also pointed to a heartening story in the North Sea in northern Europe. "There the plastics manufacturing industry uses plastic pellets that would often wash into the North Sea. Essentially, when the industry implemented a program to improve their use of pellets, the amount of pellets in the sea went down in ten years. Consequently, the amount in seabirds also went down."

If we make smart decisions about how we dispose of waste, or even how much waste we create, it might not be long until we see improvement. "If we compare this with climate change, we are talking about changing major aspects of our economy," Wilcox said. "With the plastics problem, you're really just asking people to dispose of plastics more responsibly.

"All these items were in people's hands at some point. We're really just talking about making a small change in people's behaviour."

The findings were published in the Proceedings of the National Academy of Sciences.

Seabirds and marine debris from CSIRO on Vimeo.