The yearly ritual of cleaning all of the city's major and minor nullahs and also Mithi river prior to the onset of monsoons has begun this year. Around Rs 257 crore would be spent on it, off which around Rs 82 crore will be spent on the cleaning of Mithi river alone. However, officials said that last year they had to put labourer's in three shifts as cleaning works had begun only in April. This year to avoid such a scenario, the BMC has already begun work.