本沢ダム (Motizawa Dam) – A Hidden Gem in Hachioji, Tokyo

Explore the serene waters, lush surroundings, and easy‑going vibe of one of Tokyo’s lesser‑known dams.

1. Introduction

When you think of Tokyo, neon‑lit skyscrapers and bustling Shibuya crossings probably come to mind. Yet just a short ride west of the city centre lies a completely different world—rolling hills, forested valleys, and the tranquil surface of 本沢ダム. Tucked into the mountains of Hachioji, this modest dam offers a peaceful escape for nature lovers, photographers, and anyone craving a break from the urban rush. Whether you’re a local weekend warrior or an international traveler seeking off‑the‑beaten‑path scenery, 本沢ダム is a perfect spot to unwind, snap some Instagram‑worthy shots, and discover the quiet side of Tokyo’s water infrastructure.

2. About 本沢ダム

本沢ダム (Motizawa Dam) is a small‑scale water‑control structure situated at the coordinates 35.607913 N, 139.276232 E. Built as part of the region’s flood‑control and water‑supply network, the dam plays a crucial role in managing runoff from the surrounding forested catchment. While the exact height and altitude are not publicly listed, the dam’s modest size blends seamlessly into the natural landscape, creating a calm reservoir that mirrors the surrounding trees and distant peaks.

The dam’s name derives from the local area “本沢” (Motizawa), a name that appears in historic land records dating back to the Edo period. Over the decades, the reservoir has become a favorite spot for local anglers, hikers, and school groups learning about water management in Japan. Its presence also supports downstream agriculture and helps maintain water quality for the greater Tokyo metropolitan area.

For a quick reference, you can read the Japanese Wikipedia entry here: 本沢ダム (Japanese Wikipedia).

3. How to Get There

By Train

Start at Shinjuku Station – the major hub in central Tokyo.
Take the JR Chuo Line (Rapid) toward Takao and alight at Hachioji Station (≈ 45 minutes).
From Hachioji, transfer to the JR Yokohama Line (or the Keio Line) and get off at Matsuo Station (≈ 10 minutes).

By Bus / Taxi

Local Bus: From Matsuo Station, board the community bus bound for “本沢ダム入口” (Motizawa Dam Entrance). The ride is about 15 minutes and drops you within a few minutes’ walk of the reservoir.
Taxi: If you prefer a door‑to‑door experience, a taxi from Hachioji Station to the dam costs roughly ¥2,000–¥2,500 and takes about 20 minutes.

By Car

Parking: A small free parking lot sits near the dam’s visitor area. The road is well‑marked from the National Route 16 (the main artery through Hachioji).

Practical Tips

Language: Signage around the dam is primarily Japanese, but most bus drivers and taxi drivers understand basic English. Having the address written in Japanese (本沢ダム) helps.
Timing: Trains run frequently until late evening, but the last bus back to Hachioji Station departs around 7 pm, so plan accordingly.

4. Best Time to Visit

Season	What to Expect	Why It’s Ideal
Spring (Mar–May)	Cherry blossoms begin to bloom along the reservoir’s edge, and the surrounding forest turns a fresh green.	Mild temperatures (10‑20 °C) make walking comfortable, and the pastel scenery is perfect for photography.
Summer (Jun–Aug)	Lush foliage, occasional dragonflies, and cooler waters for a quick splash.	Early mornings are pleasantly cool; evenings bring fireflies near the water.
Autumn (Sep–Nov)	Vibrant maple and ginkgo leaves create a kaleidoscope of reds, oranges, and yellows.	The crisp air and vivid colors provide a classic “Japanese autumn” experience.
Winter (Dec–Feb)	Snow‑capped hills in the distance; the reservoir often freezes at the edges, creating a tranquil, almost surreal atmosphere.	Quietest period—few visitors, perfect for meditative walks.

Insider tip: The dam’s water level can fluctuate after heavy rain. Checking the local weather forecast the day before ensures you’ll see the reservoir at its fullest.

5. What to Expect

Arriving at 本沢ダム, you’ll be greeted by a modest concrete spillway framed by towering trees. The reservoir itself is relatively calm, reflecting the sky and surrounding hills like a natural mirror. A short, well‑maintained walking path circles the water, offering several lookout points:

Observation Deck: A wooden platform provides an unobstructed view of the dam’s crest and the downstream river.
Picnic Spot: Benches and a small grassy area make it easy to enjoy a bento lunch while listening to the gentle lapping of water.
Nature Trail: A branching trail leads deeper into the forest, where you can spot native birds such as the Japanese bush warbler (ウグイス) and seasonal wildflowers.

Because the dam is primarily functional rather than a tourist attraction, there are no admission fees, souvenir shops, or large crowds. This low‑key vibe makes it ideal for:

Photography: Capture sunrise reflections, misty mornings, or autumn foliage without the usual tourist congestion.
Fishing: Local anglers often fish for carp and crucian carp; a simple fishing license (available at nearby shops) is all you need.
Relaxation: The sound of flowing water and rustling leaves creates a natural soundscape perfect for meditation or a quiet read.

6. Nearby Attractions

While 本沢ダム is the star of the day, the surrounding area offers a handful of other water‑related sites that can be visited in the same outing. All are within a 2.5 km radius, making them easy to reach on foot or by a short bike ride.

Attraction	Type	Approx. Distance from 本沢ダム	Quick Link
砂防ダム	Dam	0.7 km	(search “砂防ダム Hachioji”)
(Unnamed Fountain)	Fountain	2.3 km	(search “fountain near 本沢ダム”)
(Unnamed Weir)	Weir	2.3 km	(search “weir near 本沢ダム”)
(Second Fountain)	Fountain	2.3 km	(search “fountain near 本沢ダム”)

Note: The nearby sites are small water‑control structures and ornamental fountains that locals use for irrigation and recreation. They don’t have dedicated visitor centers, but they’re worth a quick stop for additional photo opportunities or a short nature walk.

If you have extra time, consider extending your trip to Hachioji Castle Ruins (八王子城跡) or the Takao Mountain (高尾山), both popular hiking destinations just a short train ride away.

7. Travel Tips

Tip	Details
Bring a Light Rain Jacket	Even on clear days, mountain weather can change quickly. A compact waterproof layer keeps you comfortable.
Pack Snacks & Water	There are no food vendors at the dam itself. A simple onigiri, fruit, and a reusable water bottle will keep you energized.
Wear Comfortable Shoes	The walking path is mostly paved, but the side trails can be uneven and mossy. Good walking shoes or light hiking boots are recommended.
Check the Dam’s Water Level	After a heavy rain, the reservoir may be higher than usual, offering better reflections. After a dry spell, the water may recede, exposing more of the dam’s structure.
Respect Local Rules	Fishing is allowed, but littering or feeding wildlife is prohibited. Keep the area clean for future visitors.
Timing for Photography	Early morning (sunrise) or late afternoon (golden hour) provides the softest light and the most dramatic shadows on the water.
Cash is King	Small vending machines or local shops may only accept cash, so bring some yen for any incidental purchases.
Connectivity	Mobile signal can be spotty near the dam. Download offline maps (Google Maps or MAPS.ME) beforehand.
Seasonal Festivals	Occasionally, local community groups host small events near the reservoir (e.g., autumn leaf‑viewing gatherings). Check Hachioji city’s event calendar for updates.

Final Thought

本沢ダム may not have the towering height of Japan’s famous Kurobe Dam or the dramatic scenery of Lake Ashi, but its quiet charm, easy accessibility from central Tokyo, and surrounding natural beauty make it a rewarding day‑trip for any traveler seeking a slice of serene Japan. Pack a camera, hop on the Chuo Line, and discover why this modest dam is quickly becoming a hidden favorite among locals and savvy tourists alike.

Happy travels, and may your visit to 本沢ダム be as calm and clear as its tranquil waters!