I admit that I’m a science geek. I think it’s cool to know how much oxygen is in the water and to test for it by adding various chemicals to the sample, shaking it, and watching to see the odd orange chunky floc form in the solution.

But, you don’t have to be a scientist to help collect this kind of data in Casco Bay and for it to be useful, relevant information about our coastal environment. For over 25 years, the non-profit, Friends of Casco Bay has trained volunteers to collect water samples from around the bay to monitor the health of its waters.

In fact, more than 650 volunteers have helped to sample its waters over the years. It takes that many people and many different sampling sites because Casco Bay is a big and varied place. If you look at a chart, you can see the shape of the bay stretching from Small Point in Phippsburg to Cape Elizabeth with Halfway Rock stuck roughly in the middle.

Within this 20-mile span, the depth varies greatly as does the type of bottom, which ranges from hard and rocky to squishy and silty. Then, there are the myriad factors impacting the water from recreational boating and fishing, to waste disposal and the inputs from landscaping and what we put on our lawns. All of this adds up to a great range of things that can change measurements like the oxygen levels, just to name one variable.

It is one thing to take a measurement here and there to assess what is going on, but the more critical task is to look at what changes over time and then to try to figure out why. That’s the point of this type of long-term monitoring. It can tell both the positive and negative stories.

For example, in Quahog Bay, where the water quality used to be quite poor, recent measurements show that it has improved dramatically. But in the New Meadows River, water quality has not improved. A causeway built here in 1937 to connect Brunswick and West Bath dammed the upper portion of the bay and created a restricted “salt lake” where there is now little tidal flushing. In addition, over-harvesting of shellfish 15 or so years ago not only took out the shellfish as a resource, but also removed their function as natural water filters.

So, what is good water quality and how to do measure it? Well, aside from dissolved oxygen, which is critical for marine plant and animal life, water clarity is another important factor. If those plants can’t get enough sunlight to photosynthesize, you won’t have a basis for the underwater food chain, which means very little else can survive in the bay. This is a cool one to measure, as you just lower a black and white disk into the water and see how far down you can still see it.

Acidity level is another big one. A valuable acidity measurement is the difference between morning and evening levels – which can be an indicator of the amount of plant productivity in the water. Too much productivity can lower water quality, and can occur as a result of nitrogen pollution, which can come from fertilizers.

Then, the trick is to figure out how to pull the multiple measurements together in a way that helps us understand the health of Casco Bay. To make sense of this, FOCB has come up with the Casco Bay Health Index. It combines the three major measurements into a single score and enables scientists to rank each sampling site as Good (green), Fair (yellow), or Poor (red). You can view these scores on their interactive map at www.cascobay.org/media/interactive-health-index. By clicking on each site, you can learn more about that location and also see its three measurements.

These rankings are based on data collected by volunteers over the last five years. In the big picture, many of the dots on the map are green, which is great. But, there are still areas of concern, such as those in the New Meadows and up into other riverways where human inputs and lack of good water circulation have depleted oxygen levels and reduced water clarity.

Friends of Casco Bay has also launched the “Cage of Science,” essentially a lobster trap equipped with all kinds of measurement gizmos to look at many more factors than could be taken at each sampling site. The cool thing about it is that it can record all this information on its own.

The “Cage,” designed by FOCB research associate Michael Doan, is out there independently collecting data off Cousins Island year round. This information can be used to supplement what volunteers found around the bay by providing more specific rates of change from its hourly samples.

There you have it – a basic introduction to the water quality in our bay. There is a lot to understand and we still have a lot to learn by watching how things change over time. As it wraps up this phase of water quality monitoring, Friends of Casco Bay is identifying more volunteer opportunities in data collection, outreach, and community service. You can learn more about the organization and how to get involved at cascobay.org.