NORTHAMPTON -- Police were called to Florence Monday after a Ludlow couple's casual afternoon at the Mill River turned steamy.

Northampton officers responded to Riverside Drive near Norwood Avenue at around 8 p.m. after receiving reports of a naked man and woman having sex on top of a white sedan.

Police caught them in the act, according to court documents.

At the sight of the police cruiser, the 32-year-old man pulled up his pants and 36-year-old woman went inside the car, reports said. The sedan was parked outside a row of homes about 15 feet from the roadway.

"They could be seen very easily from the roadway as you passed by," Officer Thomas Briotta wrote in a police report. "Both parties made no efforts to conceal their behavior from the public."

At first, the man told police he was changing when they arrived. But then he quickly changed his story, stating that he and his girlfriend "were doing something that they should not have been doing," court documents said.

The man went on to say that he and his girlfriend had been hanging out at the river with their three dogs, and that they had been drinking and smoking marijuana throughout the afternoon, police said.

"Things became heated and they were hot for each other," an officer wrote in a report, quoting the suspects. The couple said that they have been trying to conceive a baby.

The man and woman pleaded guilty in Northampton District Court Tuesday to disorderly conduct. and were each fined $100, court documents show.