Lake Mariam is roughly oval in shape and is on the northeast side of Winter Haven, Florida. The Polk County Water Atlas says sometimes the lake is known as Lake Marion, but a different Lake Marion is also in Polk County, Florida, where Lake Mariam is located. It has a surface area of 200 acres (809,371 m2) and is bordered on the west side, most of the south side and part of the north side by residential areas. Brandywine Health Care Center, a nursing home, is a block north of the lake. On the northwest and southwest Lake Mariam is bordered by woods and on most of the east side of the lake are woods and pastureland. On the lake's southeast side is a swampy area.