The incident happened around 6 p.m. at Lake Henry in the Continental Soldiers Park complex.
Police said the child was fishing from the shoreline when a beaver came out of the water and charged at him. The boy tried to run away but tripped, and the animal bit him in the upper thigh before continuing the attack.
A family acquaintance who was nearby stepped in to help, hitting and kicking the beaver several times until it retreated. Officials said the animal continued circling the area after the attack.
Mahwah EMS responded to the scene and took the child to Good Samaritan Hospital. There was no immediate word on his condition.
While investigating, police said they received additional reports, along with an online video, indicating the same animal may have approached or attacked other park visitors earlier in the day.
Due to the circumstances, Mahwah police contacted animal control. Responders from Tyco Animal Control arrived and observed the beaver showing signs of possible illness, officials said.
The animal was captured and removed from the park and will be sent for testing.
Authorities have not released further details as the investigation continues.
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