Authorities were notified about the incident involving a Concord woman at 11:52 a.m. After a preliminary investigation, officers believe that 67-year-old Claire Knowles was swimming in her tube and returning to shore when she “suffered a medical event”.

A 67-year-old Concord woman died Sunday after suffering a medical event while swimming in the Merrimack River, according to New Hampshire State Police.Marine Patrol officers were called at 11:52 a.m.

Claire Knowles, 67, of Concord, was swimming after an inflatable tube in mild current Sunday morning when she suffered a medical emergency returning to shore, New Hampshire State Police said.