In the meantime, the Dutch were contending with other problems. The excessive use of land for sugar cane plantation in the interior of West Java reduced the flow of water in Ciliwung River (which flows through the city of Batavia) and made the city canals an ideal breeding ground for mosquitoes, resulting in a series of malaria outbreaks in 1733–1795. This was aggravated by the fall of sugar price in European market, bringing bankruptcy to sugar factories in the areas around Batavia (the Ommelanden), which were mostly operated by Chinese labour. The unrest prompted VOC authorities to reduce the number of unlicensed Chinese settlers, who had been smuggled into Batavia by Chinese sugar factory owners. These labourers were loaded onto ships out of Batavia but the rumour that these people were thrown into the sea as soon as the ship was beyond the horizon caused panic among the remaining Chinese. On 7 October 1740, several Chinese mobs attacked Europeans outside the city and incited the Dutch to order a massacre two days later. The Chinese settlement in Batavia was looted for several days, in which 10,000 Chinese were killed. The Chinese ran away and captured Bekasi, which was dislodged by VOC in June 1741.