The East River in Chester, Nova Scotia has a watershed area of 134 km², of which 10.5% is lake surface, and drains into the East River Bay portion of Mahone Bay. It has two tributaries; Barry's Brook joins the main stem about 0.5 km upriver from the mouth, and the Canaan River joins the main stem about 4 km upriver from the mouth. The main stem, or East Branch, drains an area of 45.5 km², of which 22.8% is lake surface.

The river's water quality is impaired due to acidification, which lowers the pH to 4.7-5.0. River pH is influenced by water basin geology that consists mostly of granite and metamorphic rocks overlain by shallow soils with poor drainage, and containing many lakes and bogs.

Surveys of fish presence in East River have found Atlantic salmon, American eel, brook trout, white sucker, lake chub, banded killifish, yellow perch, and species of stickleback.

Two small waterfalls of about 2.4m in height occur on the main stem of East River, approximately 0.9 and 1.1 km upriver from the mouth. An overpass for Highway 103 about 1.3km upstream consists of five 50m long, 5m wide, and 4m high rectangular concrete box culverts. These, along with a very small waterfall at the mouth of the river, are an obstruction to upstream eel movement. This barrier to eel migration is the reason East River was chosen for the Elver Abundance Study, as the elvers cannot normally migrate past the waterfall, so the traps set below the waterfall catch all of the elvers migrating upstream.

 East River is also the location of Coastal Action's Silver American Eel Study.