Princeton’s Scenic Lake Carnegie Faces an Unwelcome Summer Visitor

Princeton, NJ -- Steve Tuorto clicked on the attachment and enlarged the photo. After studying the telltale blobs and streaks, he zoomed in on a dark green patch at the edge of the image. A new type of plankton on Lake Carnegie? No, just the shadow from a nearby tree. Tuorto closed the image and delivered his verdict.

“I can see definite signs of a potential harmful algal bloom,” he said, “But it’s hard to say without testing.”

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As the lead scientist for the water protection organization, the Watershed Institute, testing is vital to Tuorto’s work. As part of his research, he oversees the StreamWatch team whose mission is to monitor water quality across a five-county area.

Every year, from May until August, the Watershed Institute’s StreamWatch crew is on the lookout for harmful algal blooms. Caused by photosynthesizing cyanobacteria, also known as blue-green algae, these blooms can produce potent toxins with effects ranging from rashes to respiratory problems to serious neurological effects. In extreme cases, toxic blooms can be deadly.

For this reason, the StreamWatch team studies suspicious bodies of water, like the example I brought to Tuorto. Clues that might induce a scientist to reach for their sample scoop include murky green water, floating dots, emerald streaks parallel to the shoreline, or meandering slicks resembling spilled paint.

Given the signs, I was sure my photograph had hit the bullseye. It was a picture of Lake Carnegie on July 15, taken from the Harrison Street bridge the morning after a rainstorm. It seemed to bear all the marks of a harmful algal bloom – referred to by scientists as HAB.

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But I couldn’t be sure without a sample and testing of that sample by a scientist such as Tuorto. But it turns out there were signs all around telling me that this was an HAB. Literally signs. Within days of my finding that dark spot in the water below the Harrison Street bridge, orange warning signs had been posted at various spots around the Carnegie Lake shoreline -- at the boat launch area near Shady Brook Lane and by the Princeton University Boathouse, for example.

The message was clear: “Warning – Harmful Algal Bloom (HAB). Always keep children and pets away from areas with blooms or scums.” Scum – not exactly a word we want to hear when we are thinking about a water resource located literally in our community’s backyard.

Testing is believing

Cyanobacteria exist naturally in the water but are too small to see. Prime time occurs when the water warms and is suddenly loaded with bacterial nutrients. Nutritious food for a cyanoHAB — as some scientists prefer to call them — include the phosphorus and nitrogen from fertilizers, human and animal waste, and all the gunk that flows from our stormwater drains.

In other words, cyanobacteria do best when fed by the stormwater runoff of a standard suburban town.

We’re most likely to find blooms in our waterways during hot sunny summers after heavy rainfall. That’s when runoff dumps the equivalent of a bacterial feast into warm lakes and creeks, or stirs it up from the riverbed. Micro-organisms reproduce so rapidly that their population doubles every few hours. Soon their colonies are big enough for us to see, photograph, and test.

Thanks to the network of cyanoHAB testers across New Jersey, we know the prevalence of harmful blooms is getting worse. Compared to 2021 data, confirmed cyanoHABs have increased by 38 percent since 2017 when the state first started tracking them. In 2019, there were 39 confirmed blooms across the state. In 2022, there were 65. This year, there are currently 69 confirmations and we’re only halfway through the summer.

However, the NJ Department of Environmental Protection thought this summer's bloom count was in line with what they had seen before. "For comparison purposes, using July 20th as a mid-season assessment, 2024 is comparable to the previous 4 years (2020 through 2023)," said a DEP spokesperson by e-mail.

As our climate gets hotter due to the greenhouse gases trapped in our atmosphere, our waterways are getting hotter, too. This summer has broken all heat records, which may explain why cyanoHAB season seems especially active.

Since July 15—the day I took my picture for Tuorto— Lake Carnegie has registered five cyanoHAB confirmations. There are more testers on this waterway than in any others in Princeton, which partly explains the higher number of alerts. Nonetheless, the findings have triggered five localized HAB Advisories, which shows up as orange on the alert scale.

It’s not clear when Princeton University, which owns Lake Carnegie, put up the advisory signs, but they are now posted at the locations where the sampled water had been shown to be harmful – including the spots mentioned above and also on the shore of the lake by Longview Drive and where the Millstone River joins the lake near the D&R footbridge.

Orange means swimming is not recommended, boaters should be cautious, and no one should ingest the water or eat the nearby fish.

According to the New Jersey HAB Dashboard , the live database monitoring test results across the state, there’s another cyanoHAB confirmation where Harry’s Brook meets Lake Carnegie.

This same area had been sampled the week before, and registered no worrisome toxins. But like the other spots in Lake Carnegie, the July 14 rainstorm is likely to have triggered an outbreak.

Further afield in Pennington, cyanoHABs have been confirmed in Willow Pond, Wargo Pond, Honey Lake, and Rosedale Lake. Rosedale Lake, which has had persistent problems with toxic blooms over the years, was on May 28 the first waterway in our area to tip into orange.

Gift or headache?

Lake Carnegie has long been out of bounds for swimmers. It was built in 1906 as a gift to the university from the deep-pocketed industrialist, Andrew Carnegie. In the early days, swimming was permitted, but by the 1960s, complaints of sewage pollution dissuaded swimmers. Nonetheless, over the years, brave or foolhardy locals have taken the occasional dip.

Today the university prohibits swimming. However, the public is allowed to use the lake for recreation, such as fishing, canoeing, and ice skating.

Its prime purpose, and the reason that stretch of the Millstone River is a lake at all, is because it is a dedicated resource for the university’s row team.

Indeed, when I asked the university many months back why swimming was not permitted in the lake, the response from university spokesperson, Michael Hotchkiss, was this: “Swimming in Carnegie Lake would be inconsistent with its primary use as an intercollegiate rowing facility.”

Hotchkiss did not answer questions about the quality of the water inside the lake. This may be because Lake Carnegie’s water quality has long been worrisome. Since 2002, it has been classified as an “impaired” water body. This means the water should not be used without restrictions.

Carnegie’s lavish gift to Princeton isn’t alone in this designation. Most water bodies in New Jersey are impaired, including all 12 waterways in the 08540 zip code .

We can mostly blame humans. Or more specifically, everyday human activities in a heavily built-up state, the effects of which eventually trickle down to the waterways.

As with the accelerants for a cyanoHAB, the contents of stormwater runoff, farm and yard fertilizer, leaks from sewers and septic tanks, and the questionable chemicals sloughing off our trash, all contribute to New Jersey’s dirty waterway brew.

Another big contributor is the E.coli bacteria from animals’ digestive tracts. In Princeton, the large populations of Canada geese on the banks of lakes and streams is especially responsible for boosting the toxic load.

The Watershed Institute can say precisely what that load is. Like the cyanoHAB team, another group tracks additional quality indicators to gain an overall picture of water health. Every Sunday, the StreamWatch Bacterial Action Team samples most freshwater bodies in central New Jersey. They study the water temperature, E. coli levels, and turbidity, as well as the levels of chloride, phosphate and nitrate.

The data are recorded on a live tracker, the StreamWatch Dashboard .

This summer’s data so far shows moderate indicators in most of Princeton’s waterways, with the exception of high temperatures and occasionally spiking E. coli levels. All waterways show persistently high chloride levels. This is likely the result of the rock salt used to de-ice roads in the winter and which, like all contaminants, eventually wash into the nearest stream.

The Watershed Institute’s weekly data will eventually feed into a Clean Water Report Card , which is issued annually for each municipality in central New Jersey.

Last year Princeton’s waterways scored a middling grade. A key contributor to our less-than-stellar report was our high levels of phosphate, chloride, and E. coli. In other words, cyanoHABS are only a small part of Princeton’s water quality woes.

Fixing the problem

The causes of our impaired waterbodies is complex, as are the fixes. This may explain why in response to several questions about the latest cyanoHABs on Carnegie Lake, Princeton University spokesman, Hotchkiss, simply replied: “Princeton University continues to work closely with the NJ Department of Environmental Protection to monitor and address algal issues in Lake Carnegie.”

While the university owns the lake itself, the quality of the water in all waterways is a matter of public concern. It thus triggers many levels of involvement. Not only is drinking water sourced from the same freshwater sites that are often classified as impaired — most of Princeton’s waterways drain into the Raritan River system, for example, which provides our drinking water — but long-term pollution has impacts on groundwater and surrounding ecosystems, too. All levels of government and society are implicated in the availability of clean water.

Indeed, the state has already expended millions in efforts to understand and combat the increasing prevalence of cyanoHABs. Research is just getting started on how cyanotoxins impact groundwater and long-term public health.

Closer to home, the Princeton municipality is focused on upgrading both stormwater and wastewater infrastructure, in part to keep contaminants from reaching the water. Both the town and Princeton University are also investing in green infrastructure, such as rain gardens and native plants, in a bid to absorb rainfall before it reaches the lake.

As for the cyanoHABs popping up in Princeton this summer, Tuorto emphasized the big picture.

If we see cloudy green water and think we have nothing to do with it, we’re deceiving ourselves, he advised. We only have one water source and whether we collect it directly from the lake or get it from a reservoir first, it carries everything we do to the land. If our actions don’t directly impact us, they will certainly impact someone downstream.

“I believe clean water is a privilege,” Tuorto said. “I also believe we have to earn it.”

The Watershed Institute’s driving philosophy is that restoration of our waterways is possible. It can be done through more science, more advocacy, and more citizens having big picture thoughts about the water that they might otherwise take for granted.

Carolyn Jones is a freelance reporter based in Princeton. She can be found at www.carolynjoneswrites.com .

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