Environment Secretary Michael Defensor has ordered a ban on the construction of new fish pens and cages at the lake to prevent an ecological disaster, the department said in a statement.

Any illegal structures used for the captive breeding of fresh-water fish will be demolished, he added.

It said pens and cages now take up more than 10 percent of the surface area of the 90,000-hectare (222,300-acre) lake, situated on the eastern outskirts of Manila.

"Water quality in several portions of the Laguna Lake is deteriorating due to siltation, sedimentation and domestic waste," Defensor said.

Fish pens and cages were identified as major contributory factors that affect both water quality and navigational activities in the area, he added.

"Fierce competition for the lake's aquatic resources plus harmful fishing activities and practices strained the lake's natural carrying capacity," Defensor said.

Fish culture was introduced at the lake in the 1970s

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