Tidal access to Bolsa Bay, California, was removed in 1899 then partially returned in late 1978. Investigation in 1977-1978 revealed that salt marsh vege- tation had adjusted to lowered water levels and subsidence by establishment of zonal patterns at anomalously low elevations. Net production in macrophytes decreased with elevation (4380 to 164 g rrr 2 yr _1 ), soil nitrogen (NH 3 ) remained high at all levels, and soil salinity was seasonally variable (7 to 54 ppt). Low redox potentials indicated persistent anaerobiosis. With the recent removal of tide gates and return of tidal fluctuation, much of the pre-existing marsh has been drowned.