The Massachusetts Department of Conservation and Recreation (DCR) manages Otis Reservoir and Tolland State Forest. Here's the link for this specific park on the Mass.Gov web site:
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Otis Reservoir Dam was built in 1865 and is a composite earth and stone masonry dam, about 630 ft. long with a maximum hydraulic height of 31.5 ft. It is classified as small in size. This information was taken from the CORPS OF ENGINEERS WALTHAM MA NEW ENGLAND DIV.
A full description of the dam can be found in BUILDING OF THE OTIS RESERVOIR Otis, Massachusetts Excerpts From: Samuel Watkinson Collins Memorandums (Co-Founder of The Collins Company, Collinsville (Canton), Connecticut)
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The trail to the cache runs along the east side of the river beneath the outflow of the reservoir. The amount of water exiting the reservoir varies throughout the year and is the least in spring when water is allowed to rise in the reservoir. The water level rises 8 feet in the spring for the boating season and falls 8 feet in the fall to protect the docks from ice damage in the winter. The main trail is 6 feet wide and runs on a ridge above the river. It is relatively easy to hike but the real beauty of the area can be enjoyed from the many small footpaths that lead to the rivers edge. Just beneath the dam, the views of the gorge and waterfall areas are magnificent but the area can be dangerous with slippery rocks, high drop offs and downed trees. These paths are not suitable for young children or pets. The footpaths below the falls are less dangerous although slippery surfaces abound. When I first viewed this area, I was struck with a feeling of primordial enchantment. Maybe it was the day or the light, you can judge for yourself.
Parking is available at the trailhead on a gravel pull off that easily holds two cars. It is located across the street from the marked trail.
The cache is full of cache type items, a log book and a my newest TB. The GPS readings were very flaky and I averaged readings from 2 separate days. Please feel free to post your readings if significantly different. A FTF prize is included with the log book. Dress appropriately for a hike in the woods with special attention to bug spray and/or tick precautions.