Ecological Studies of the Saw Kill – 2020 Summary

Erik Kiviat, Hudsonia

Hudsonia has continued the Saw Kill studies initiated in 2017 in connection with Bard’s exploration of microhydro power on the stream. The accompanying report relates our findings in 2020. Despite hindrances and delays due to pandemic restrictions, we were able to achieve good results.

American Eel

The American eel is a Species of Greatest Conservation Need (SGCN) in New York. A June trapping survey in the pool immediately below the Annandale Dam revealed that the habitat is used by modest numbers of American eels. We caught one very large eel that measured 90 cm total length, which could be the largest eel ever documented in the Hudson River watershed. Four other fish species and a crayfish were also documented; these are common species in the Saw Kill.

Bob Schmidt and Lea Stickle installing the eel trap just below Annandale Dam on June 8, 2020.

Louisiana Waterthrush

This warbler is also a SGCN in New York. Almost annually since the 1970s, Louisiana waterthrush has been heard singing just below the Lower Dam. Although some activity was detected farther upstream prior to 2020, last year the only waterthrush found was in the traditional spot at the largest waterfall, where nesting likely occurs.

Wood Turtle

There is a historic record of this New York Special Concern species near the Saw Kill at Bard College, and recent documentation of a population in the Saw Kill farther upstream. We conducted a wading and walking survey for wood turtles on the Saw Kill from below the Lower Dam to Route 9G on 7 and 15 October 2020 during the time when wood turtles would have been in the stream channel rather than in their summer riparian habitat. No wood turtle was found. However, we rated the habitat as of good quality and likely inhabited by small numbers of wood turtles.

Flora of the Saw Kill

In summer 2020, we performed a survey of higher plants, repeating the study of a few years ago. Special attention was directed to winged monkeyflower, a rare species in New York. The two stands of winged monkeyflower, located between the Lower Dam and Annandale, are doing well, although deer grazing was evident in one stand. Although several localities for this plant were found in the Hudson Valley during the last few decades, the current status of most occurrences is unknown. This may make the Saw Kill stands especially important.

Winged monkeyflower (photo by Gretchen Stevens).

Water Quality

In spring 2020, the data sonde was redeployed in the Saw Kill just above the Annandale Dam. This instrument measures several water quality variables continually at 15 minute intervals. A second sonde collects data on the upstream side of the Lower Dam. These measurements allow us to see not only the ordinary, day-to-day conditions of the stream, but also intermittent peaks or troughs in water quality due to intense runoff or other events upstream.

Water temperature in the impoundment above Annandale Dam during the 2020 (blue) and 2019 (red) field seasons.
Specific conductance in the impoundment above Annandale Dam during the 2020 (blue) and 2019 (red) field seasons.

Potential Impacts of Microhydro Power Development

The principal reason for the studies summarized here is to anticipate and document impacts that may occur as a result of installing turbines driven by flow at the Annandale Dam. We do not anticipate important impacts to the wood turtle, Louisiana waterthrush, or winged monkeyflower. Wood turtles are not likely to be disturbed by minor changes in hydrology. There is some possibility of hatchling wood turtles, or other hatchling turtles, being impinged or entrained at the water intake for the turbines. The waterthrush and monkeyflower are far enough downstream, so far as is known, that impacts are unlikely. Plants that occur in the Annandale Pond near the dam, or on the stream banks between the dam and River Road, are common species that should be robust to the proposed installation and operation of the turbines, with the exception of some potential loss of vegetation if localized dredging occurs for the water intake.

Eels entering the upstream or downstream ends of the turbine system, or possibly other effects on eels, are the main ecological concern. We understand that the hydropower project is being designed to reduce the risks and mitigate impacts to eels.


The 2020 studies were performed by Hudsonia staff and collaborators including Chris Graham, Erik Kiviat, Susan Rogers, Bob Schmidt, Gretchen Stevens, Lea Stickle, Jason Tesauro, and Emily White. Our work was conducted with funding from Bard College under a grant from the New York State Energy Research and Development Authority for a microhydro power demonstration project. Please see the full report for details.