Beaches in the Australian city of Sydney have reopened for swimmers after being closed earlier this week when thousands of mysterious black tar-like balls washed ashore, prompting health concerns.

Beaches in Sydney reopened after being closed earlier this week when hundreds of mysterious golf ball-sized black lumps washed ashore. These dark spheres, which were first spotted on Coogee Beach on Tuesday, were confirmed to be “tar balls” but it was unclear where they originated from.

Sydney beaches reopened on Saturday after thousands of tar balls had been washed ashore earlier this week. Since Tuesday, little balls made up of oil, debris, and other pollutants have littered popular eastern suburbs,

Beaches throughout Sydney’s eastern suburbs are reopening for the weekend and the city’s annual Sculpture by the Sea exhibition. Beaches in the Randwick and Waverly council areas were previously closed after the discovery of tar balls along the shoreline.