The haze in Singapore is largely caused by forest fires in Indonesia, particularly in Sumatra and Kalimantan islands, which are often associated with wildfires and the burning of large tracts of forested land for agricultural purposes, such as palm oil and pulpwood plantations, using the slash-and-burn method. The haze usually occurs during the southwest monsoon season, which runs from June to September. The smoke from these fires drifts over the border and engulfs much of the region, posing a threat to public health, education, and businesses such as tourism. The haze can cause air quality to reach hazardous levels, which can lead to health problems, especially for those with sensitive conditions. The Singapore government has introduced the Transboundary Haze Pollution Act 2014, which criminalizes activities overseas that contribute to haze, to mitigate the regional issue.