A frontal structure in Liverpool Bay was studied using conductivity-temperature-depth (CTD) and current meter data. At times of weak vertical mixing by wind and tides, a density-driven gravity flow, induced by river discharge, distorts the thermohaline field, so that an expanding stratified region develops, bounded offshore by a surface front. Expansion of this frontal structure is increasingly curbed by rotation as a near-geostrophic balance is attained. Owing to friction, the space scale and time scale of frontogenesis are somewhat greater than two internal Rossby radii and an inertial period, respectively. At times of increased mixing, the frontal structure is destroyed and the enhanced friction between layers inhibits gravity flow, hampering the frontogenesis mechanism. Large variability in mixing conditions results in an intermittent frontal structure. ¿ 1998 American Geophysical Union