MILWAUKEE (AP) — Authorities say three people died in snowmobile accidents last weekend, boosting the number of deaths to 17 for the season.

The Wisconsin Department of Natural Resources said all three of the victims were from Illinois. Two of them died after striking trees and one person was killed after being struck by another snowmobile rider, the Journal Sentinel reported.

There have been nine fatalities this month. That includes a 15-year-old Wisconsin boy who failed to stop at an intersection of a public trail and highway and collided with a car, a 28-year-old Wisconsin man who struck a fence on private land and a 29-year-old woman who struck several trees.

Alcohol, excess speed and driver inexperience are the leading causes of snowmobile accidents, according to the DNR.