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How healthy is Casco Bay?

Our most frequently asked question

“How clean is Casco Bay?” is the question we are most frequently asked. And it is a good question. What does clean mean to you?

Thanks to advocacy under the Clean Water Act, we have decreased bacteria and toxic pollution flowing into Casco Bay. As the guardians of a healthy Bay, we say, water clarity and oxygen levels have improved in many parts of the Bay but in other areas, low oxygen, increasing acidity, and murky water are cause for concern. We are also seeing more frequent nuisance and harmful algal blooms and excess nitrogen.

In problem areas, low oxygen levels, murky water that prevents sunlight from penetrating deep into the water, and rising acidity levels are recipes for troubled waters. We may not always be able to identify the causes of these changes, but our monitoring efforts do show where problems lurk.

 

How do we know about the health of the Bay? For over 30 years, we have been testing its water quality, measuring salinity, dissolved oxygen, water temperature, water clarity, pH, and since 2005, nitrogen. You can learn more about our science here.

By monitoring the health of specific sites around the Bay, we can then ask:

  • What are the relative conditions of sites across a region?
  • Which sites require a closer look?
  • Do conditions at each location seem to be improving or degrading over time?

What are the biggest threats to the Bay today?

Excess nitrogen, ocean and coastal acidification, stormwater pollution, climate change, and a lack of government resources to tackle these issues threaten the health of Casco Bay. As local, state, and federal governments’ budgets shrink, we are mobilizing more volunteers than ever to monitor water quality and help clean up our shorelines. We are investigating innovative and collaborative ways to address these issues. You can learn more about the threats to Casco Bay here.

Help us tackle the biggest threats to the Bay

Cover photo: Photograph by Kevin Morris • Aerial support provided by LightHawk

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