I recommend against ever using a complete divider. A complete divider which prevents water getting through, generally backfires. Condensation or movement of animals inevitably carries water to the land side, where it accumulates to form a bog, while movement of the animals carries land particles into the water, producing a similar effect. Better to have a porous barrier which allows two-way movement of water, and a pump concealed somewhere within the land. That barrier can be as simple as a pile of rocks holding back a bed of gravel or LECA. By hiding the pump under the land, particles of soil will be drawn from the open water back under the land mass, while water can be pumped from under the land to prevent stagmation. Your land area becomes a filtr for the water and you have no stagnant and hard-to-clean areas.