A member of the public spotted the line and tape strung between two power poles on the intersection of Branksea and Eddystone Sts while driving through Kaitangata at 9pm on Tuesday.
He removed the device and handed it to police.
"It was tied at neck height for a cyclist or someone riding a motorbike," Const Taylor said.
"Police are concerned about it."
Const Taylor said once the line had been tied between the poles, there was no way of controlling who ran into it.
"The fishing line could have done some serious damage, and could cause them to crash."
Const Taylor said it was the first time he could recall this happening, "and we don't want a repeat".
Lawrence police arrested a 23-year-old Dunedin man at 7am on Tuesday after a Bowlers Creek resident reported the man had driven into their letter box and then hit a road sign.
Senior Constable Robert Wallace said the man was processed for drink-driving.
He is due to appear in the Balclutha District Court on April 20.
Milton police are looking for information about the theft of three mountain bikes from properties around Milton in the past few weeks.
Constable Brian McKinney, of Milton, said a Marin bike worth $1500 was taken from a Burns St property on March 22, a child's Milanzo bike was taken from an Ajax St address on April 2, and a yellow and red women's mountain bike was taken from a shed on Johnson St on April 4.
Milton police are also seeking information relating to the theft of 1000 litres of diesel from a farm tank on Akatore Rd on Saturday night or Sunday morning.
An attempt was also made to steal 1500 litres of diesel from a tank at the Gorton Timber sawmill earlier this week.
Anyone with information can contact the Milton police on (03) 417 8203, or call crime-stoppers anonymously on 0800 555 111.
