1.   Environmental groups have long complained that open lagoons pose a risk of spilling nitrogen-rich waste into waterways.

2.   We sailed slowly up the channel and into an open lagoon studded with small islands of mangrove.

3.   Currently, most hog waste is broken down in open lagoons by bacteria that do not require oxygen.

4.   For example, they said, the EPA proposal stopped short of banning the use of open lagoons for wastes.