Cannabis growers are being arrested in the Netherlands as Dutch police locate their supplies easier than ever before. The Independent is reporting that the lack of snow on the roofs remains a telltale sign of drug lords in the area, because the warmth that is needed for cannabis plants to grow is enough to melt the snow on the property’s roof. This, for police suggests that they have more than just poor insulation in their homes.

Cannabis arrests have been recorded up and down the country since the snow started to fall. A farm in Zutphen contained over 88 marijuana plants which resulted in several arrests on Wednesday.

Officers in Amersfoort also discovered an illegal farm on Monday which contained over 500 cannabis plants. The estimated value of these plants is well over £37,000 (about $57k). Officers decided to investigate the property when they found out that the roof was devoid of snow, and remarkably dry when compared to other properties in the area. The plants themselves were destroyed, and police called on local residents to inform them of any snow-free rooftops.

Twitter users then went on to say that innocent families could well be targeted if they have had a recent loft conversion, and that a snow-free rooftop should not be enough to assume illegal activity.

The Netherlands has well known liberal laws regarding cannabis. However, it’s currently illegal to grow more than five plants in any single household.

With snowfall dropping off in the area, police are now resorting to heat detection equipment to uncover farms. This equipment can detect heat from thousands of feet away.