Alcove of nearly pure groundwater, fueling growth of purple cyanobacterial mats that then spill over the walls into the Arena.Middle Island sinkhole is open to Lake Huron creating a gradient of biological activity.

Figure 2: (Top image) From inside the Alcove, the nearly pure groundwater that fuels purple cyanobacterial mats spills over the wall into the Arena (photo by Russ Green, Thunder Bay National Marine Sanctuary). (Bottom) With a 9-meter (25.5 foot) long Boston Whaler for scale, the Middle Island Sinkhole is open to Lake Huron, creating a gradient of biological activity (aerial photo by Scott Kendall and Bopi Biddanda, Grand Valley State University).

Related Links

Thunder Bay Sinkholes 2008

Thunder Bay Sinkholes 2008: Mission Plan

NOAA Ocean Explorer Gallery

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