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Lake Bernard Frank (Lake Frank), is a 54-acre (220,000 m2) reservoir on the North Branch of Rock Creek in Derwood, Maryland, United States, just east of Rockville. It is named after Bernard Frank, a wilderness activist and a co-founder of The Wilderness Society. The lake's boundaries are, approximately, Route 28, East Gude Drive, Avery Road, and Muncaster Mill Road. Lake Frank was created in 1966 to aid in flood and sediment control, as well as to provide recreation. It has an earthen dam, installed in 1967, on its southern side. It was created as a sister lake to Lake Needwood. Lake Frank is owned by the Maryland-National Capital Park and Planning Commission (M-NCPPC).
The lake's secluded location within Rock Creek Regional Park is another of its assets. Visitors to the lake must bike or walk about 1/4 of a mile from all parking lots to get to the lakeshore. The Lake Frank & Meadowside Trails surround the lake, making it a favorite hiking spot. Also, locals enjoy fishing from the shoreline, though a license is needed to do so. However, swimming, boating, and ice skating are prohibited.
The main trail around Lake Frank, the Lakeside Trail, is a 3¼ mile long loop. Approximately 2/3 of the trail is unpaved and traverses through the woods surrounding the lake. The other part of the trail is wider and paved. At the approximate half way point of the trail, there is a creek that must be crossed. Though there are a group of rocks which form a bridge-like path across, the creek may be unpassable for some depending on the water level.
Water Quality 
Recently, pollution of the lake has been slowing, in contrast to previous years. In 1998, the Maryland Department of the Environment (MDE) identified Lake Frank as "impaired by nutrients" on its list of impaired surface waters. Eutrophic conditions in the lake were described at that time, evidenced by excessive algal growth and low dissolved oxygen levels. In 2002, MDE prepared a report based on more recent monitoring data which indicated improved conditions. The 2002 report proposed that the lake be removed from the impairment listing.