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Porters Lake on Nova Scotia's Eastern Shore, is a 20 km long estuary open to the Atlantic Ocean at the southern end. Due to fluctuating sea levels and changing configurations of the coastline since the end of the Wisconsinan glaciation, the lake has experienced both freshwater and estuarine conditions. For the last 300-500 years the lake has been undergoing marine intrusion due to the rising relative sea level. The foraminifera and "thecamoebians" (or arcellaceans) from the surficial bottom sediments form several distinct assemblages that can be related to the degree of restriction of each of the four basins of the lake. Results from several sediment cores indicate a freshwater phase in the lake immediately following deglaciation, a marine intrusion commencing c. 2000 years B.P., another freshwater phase, and the second marine intrusion c. 500 years B.P., related to submergence of a sill at Rocky Run. The earlier marine influence has been correlated with a bedrock channel which formerly connected the lake with the Atlantic. This was revealed by seismic data collected beneath present-day Lawrencetown Beach, a large coastal barrier beach.

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