A 17-year-old boy was left with serious wounds to his back and face after an attack at a reservoir on Saturday night.
He was assaulted with a knife or another sharp object in what police believe was an unprovoked incident at a reservoir between Townhead and Glenboig, near Coatbridge.
The teenager had to be taken to Monklands Hospital for treatment.
Sometime between 8pm and 9pm on Saturday, at the body of water near the Heatherbell level crossing, there was a large group of young people.
Officers are keen to speak to anyone who may have seen the attack, but are also looking for two particular teenage boys.
The first is described as between 14 and 17-years-old, 5ft 5in tall, of skinny build with short dark hair with a longer fringe at the front. He was wearing a bright orange top and glasses.
The second boy is thought to be around the same age and was wearing a dark-coloured tracksuit with a hood and may have had a black eye.
Detective constable Nicola Bonnar, of Coatbridge CID, said: “This is believed to have been an unprovoked attack that has left a 17-year-old with serious injuries that required hospital treatment.
“There were a large number of youths in the area at the time and we are keen to speak to anyone who saw what happened or knows the two teenagers described.
“If you can help with our enquiries then please contact us on 101, quoting incident 2189 of Sunday, August 29, or make a call anonymously to the charity Crimestoppers on 0800 555 111.”