Illegal mining of sand from riverbeds and banks to feed the construction boom has once again become rampant in Ernakulam district, posing a serious threat to the very survival of rivers.

S. Sitaraman, environmentalist, said that after a brief period when honest police officers had kept a tight leash over the menace by taking stern action against the offenders, the problem had re-emerged in many pockets in the rural areas of the district.