The article discusses how river mouth deltas in Lake Biwa change over time, focusing on the Fujinoki river mouth delta. The researchers used aerial photography, daily photography, and sediment analysis to study the delta's development. They found that the delta's shape changes daily and seasonally based on water levels and river runoff. The delta grows and shifts throughout the year, with different patterns in each season. Sediment characteristics were also analyzed to understand how the delta forms and changes.