Montclair-area environmental activists and state officials are trying to figure out the cause of a May 10 fish die-off in the Third River, which the activists describe as having a “devastating impact” on the local waterway. 

“We had a severe die-off, where what we believe is the entire population of fish in the river just suddenly turned up dead,” Jonathan Grupper, member of Friends of the Bonsal Preserve, said.   “Part of what was really tragic about that was realizing how many species of fish and aquatic lives the river consisted of.” 

A woman alerted Grupper after she saw dead fish on the river banks, he said. 

Ever since, Grupper and the New Jersey Department of Environmental Protection have been trying to figure out the cause. And that means looking upstream, Grupper said. 

“Over the years we've tried really hard to get to know all of the impactors upriver from us so that we can engage them and make sure that they are aware of any kind of impacts they might have,” Grupper said. 

Those upriver include Department of Transportation projects on Route 46, by the river’s headwaters, the Montclair Beach Club and a Newark water treatment facility on Valley Road.

But the people with the biggest impact on the river are Montclair residents and their lawn fertilizers, Grupper said. The fertilizers contain nitrate, which washes off lawns into the river, and creates “severe oxygenating events,” he said. 

“They create an algae bloom,” Grupper said. “It sucks the oxygen out of the river.”

Grupper and Friends of the Bonsal Preserve want residents who live alongside the river to know that using lawn fertilizer can kill fish, he said. 

“We would like them to do a better job of working with their landscapers and making choices that are environmentally friendly,” Grupper said. “If you live near the river, that's your responsibility.”

The May 10 die-off could have been from lawn fertilizers, but it could have been from a different pollutant or it could have been from multiple pollutants, Grupper said. 

Dead fish swept up on the banks of the Third River earlier this month after an unknown pollutant caused a fish die-off in the Montclair waterway. (COURTESY ANNA DRUKKER)
Dead fish swept up on the banks of the Third River earlier this month after an unknown pollutant caused a fish die-off in the Montclair waterway. (COURTESY ANNA DRUKKER)

“The best we can do is go back to the folks who are possibles and ask that they'll be honest with us and tell us where they made a mistake,” Grupper said. “So we can make sure it doesn't happen again.”

A DEP representative visited the river on Thursday, May 12 and is looking into the cause of the die-off, Grupper said. 

But the DEP likely missed the opportunity to collect a helpful water sample, since the visit came days after the pollutant entered the river and was washed downstream, he said.

“It's like if you came up on a crime scene, and it was stripped of any clues,” Grupper said. “It's maddening.”

But nonetheless, Grupper said Friends of the Bonsal Preserve is happy about the DEP’s involvement. 

“We're excited about having their attention and help and their acknowledgement of the urgency,” he said. “It’s gone a long way for us.”

DEP Public Information Officer Caryn Shinske told Montclair Local this week she was checking on the department’s role in investigating the die-off. Montclair Local is awaiting a further response.