From: Frederick Law Olmsted and the Boston Park System by Cynthia Zaitzevsky (Recommended Reading)
The Fens was completed at the time of Mr. Olmsted’s retirement in 1895, but the salt marsh design survived for only another 15 years. There had been problems almost from the beginning, for the tide and flood control system, so carefully worked out by Mr. Olmsted and Joseph Davis, the city engineer, had been misused and over loaded.
When the Charles River dam was completed in 1910, the water flowing into the Fens from the Charles River was fresh instead of salt, thus rendering the entire design obsolete. Although John Charles Olmsted (nephew and step-son), Frederick Law Olmsted, Jr. (who joined the firm in 1895) and Arthur Shurcliff (a former student of Mr. Olmsted’s) made detailed recommendations to the park commission for the redesign of the Fens in that year, no action was taken.
Instead the Fens was used as a kind of dumping ground for fill from other projects, such as the excavation of the subway (Park Street Under to Cambridge subway). In 1921 Shurcliff, again with the Olmsted Brothers as consulting landscape architects, prepared plans and a report for a comprehensive redesign of the Fens that would violate as little as possible the visual character of the original design while adapting to changed conditions. But again no action was taken.
Of Mr. Olmsted’s original design for the Fens little is left today, other than the general boundaries, two major bridges, the Stony Brook gatehouse and some original trees. The marshes are, of course, gone, and most of the waterways have been altered. It is futile to regret the original salt marshes and salt-water vegetation, since the damming of the Charles River was necessary and inevitable. On the other hand, the failure to carry out a comprehensive new design for the Fens after the dam was built was a SERIOUS error of judgement.
Today the Fens is a rather peculiar collection of spaces that appear to be connected entirely by accident.