Shellfish harvesting has been shut down temporarily along two areas of Casco Bay as an algae bloom threatens some marine life.

Starting Saturday, Maquiot Bay in Brunswick and the eastern side of Middle Bay in Harpswell will be closed to shellfish harvesting.

It comes amid the spread of a phytoplankton which isn’t harmful to humans, but can kill shellfish and other marine life.

The bloom can now be seen from the New Hampshire coast to Penobscot Bay.