Tolo Harbour is a landlocked bay with poor tidal flushings in the northeastern part of Hong Kong. During
the 1980s, excessive nutrient loading led to dramatic increase in nutrient concentrations, accompanied
by lower N:P ratios, higher algal biomass and shifts in the phytoplankton community. We studied the
effects of nutrient loading reduction measures on nutrient concentrations, nutrient ratios and phytoplankton
dynamics in Tolo Harbour by comparing data collected before the full implementation of
nutrient loading reduction measures (1986e1997) to those after the implementation (1998e2008). Such
measures led to declines in nutrient concentrations, changes in N:P and N:Si ratios, lower chlorophylla
concentrations and fewer algal blooms. Diatoms were the most abundant phytoplankton group in Tolo
Harbour both before and after declines in nutrient concentrations. The density of dinoflagellates did not
change, but substantial increase in other algal group abundance was recorded.