A Lake Erie algal bloom is so big it could be seen from space.

Satellite imagery captured a severe bloom of blue-green algae that started spreading across the western half of Lake Erie in July 2019.

This image shows the bloom on July 30, as observed by the Operational Land Imager on the Landsat 8 satellite.

The green patches are where the bloom was most dense and where toxicity levels were unsafe for recreational activities.

The bloom covered about 300 square miles of Lake Erie’s surface when the picture was taken, according to news reports. The algae had spread across 620 square miles by Aug. 13.

While blooms in Lake Erie are common in the summer, NOAA researchers forecasted that 2019 could bring some of the most abundant blooms in recent years.