A man flashed at a woman while she was out walking her dog in Fairhaven, say police.
The woman was walking near to Fairhaven Lake on Tuesday, November 21 at around 12.30pm when a man approached her.
According to police the man then exposed himself and began a sexual act in front of her.
Police are now appealing for a birdwatcher, who was in the area at the time but not believed to have been involved, to get in touch.
A spokesman for Fylde Police said: "We are appealing for information relating to a sexual assault.
"The victim was a lone female who was walking her dog, she was approached by a male who exposed himself and began a sexual act in front of her.
"The male was described as a white male, 50 - 60 years, average build with wavy hair and a goatee beard.
"We are aware that another male was in the area at the time who is not connected to this incident, he was bird watching near to the steps from the beach near the grass verge.
"We would appeal for the bird watcher to come forward and anyone else to contact us who may have information."
Anyone with information is asked to contact police on 101 quoting WA1721862.
Alternatively you can contact Crimestoppers anonymously on 0800 555 111 or on-line at http://socsi.in/zCU3Q.