Bde Maka Ska's Reputation for Clear Water, and the Asterisk on It

Bde Maka Ska, the largest lake in the Minneapolis chain and the system's center for swimming, sailing and paddling, has long held a reputation for clear water. The Minneapolis Park and Recreation Board's assessments rate it consistently excellent for aesthetics and clarity, with low bacteria levels most of the time.

That clarity is not automatic for an urban lake. It reflects the broad restoration that lifted the whole chain, alum treatments to bind phosphorus, constructed wetlands, storm-sewer work and shoreline rebuilding, layered on the lake's natural advantage as a large, deep, well-mixed basin that resists the worst of summer's algae blooms.

The asterisk on that reputation is erosion. According to the Park Board, high water levels in 2014 increased beach erosion at Bde Maka Ska and may have contributed to elevated E. coli, enough to pull the lake's public-health rating down to "good." A bank that crumbles into the water does not just look worse; it can carry bacteria and sediment straight into the swimming area, tying the lake's clarity to the stability of its shore.

Bacteria also spike with heavy rain. The Park Board tests lake water weekly for E. coli and closes beaches when readings run high, reopening them after resampling shows the level has dropped. In recent wet summers, closures at Bde Maka Ska's North, 32nd Street and Thomas beaches, often alongside beaches at Lake Harriet and Lake Hiawatha, have followed periods of heavy rainfall.

The forward question is whether wetter, flashier weather will test that reputation harder, which is what makes the Park Board's shoreline-stabilization work a quiet investment in the clear water the neighborhood takes for granted.