An underwater video system (Video In Situ:VIS) is described that deter
mines sizes and settling velocities of suspended mud flocs in situ, wi
thout disturbing large fragile aggregates. Some results are presented
from the Ems estuary, showing macroflocs of 200 to 700 mu m (up to 1 m
m) diameter with settling velocities in the range of 0.5 to 8 mm . s(-
1). They survived high current velocities of >1 m . s(-1).