Sagami River 相模川 originates from Oshino-hakkai 忍野八海, a vast welling of water where rain and snow falling on Mt Fuji comes out to the surface. It then flows to the east through a narrow valley between Okutama Mountains 奥多摩 and Tanzawa Mountains 丹沢. Infuriatingly for Tokyo, it then turns right, er … to the south I mean, in Sagamihara City which is right in front of Tokyo. (“Oh, if it came to our direction, our water problem would be blah-blah-blah,” you know?) The river runs through so-so-suburban area of Kanagawa, then pours to Sagami Bay near fashionable beach resorts. The way the river flows like
(1) Upstream goes through the relatively flat mountain plateau of Mt. Fuji, which is in Yamanashi Prefecture 山梨県,
(2) Midstream runs through mountainous area, which is like upstream for the other rivers, and
(3) Downstream passes between large human settlements, in a more relaxed manner.
So, for the case of Sagami River, typical feature of nature for “upstream” can be seen in the midstream along Route 20, aka Koshu Kaido Highway 甲州街道, the north-most part of our prefecture. We people of Kanagawa normally get the image of Sagami River from its “downstream” flow, after turning right in Sagamihara. The forests we find along the downstream of Sagami River are often satoyama-kind (in relatively higher altitude) or the city parks. Inevitably, collecting specimens from such part of the river is different from the way we take in Yadoriki Water Source Forest やどりき水源林.
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| Sagami
River at a bit upstream from Tomei Ebina JCT. Here is about 11km upstream from the mouth of the river to Sagami Bay, i.e., the downstream part of the river. |
Today, I tell you my adventure in one of such spots of Sagami River. It was near Higashi-Oshima Camping Ground of Sagamihara City 東大島キャンプ場. The spot we’ve done our research was not in the Camping Ground itself, and I won’t tell you where exactly. Reason? Yeah, the place is right after the Sagami River turns to the south after Lake Tsukui 津久井湖 / Shiroyama Dam 城山ダム. There, the mainstream of the river has lots of water. It flows relatively rapidly. It is not advisable for anybody jumping into the water as it is too risky. Besides, doing fishing at that place needs to purchase fishing rights from the local Fishery Cooperative. I don’t think it is much of the info for you without the explanation of such business deals … (If you want to purchase a day pass for fishing near the camping ground, the Office of Higash-Oshima Camping Ground has an info. Good luck.) In any case, we did not wade in the mainstream of Sagami River, but did our study in a sidepool. There is a spring gathering water from satoyama forests near the Camping Ground. The water from these ag-area first come out to the ground from the spring, then pours into the mainstream via a small exit. Its small bank is full of water-loving grasses and aquatic plants. Such vegetation can also be found along the mainstream, but inside the pool has far more calmer flow. That’s the point for aquatic creatures to survive.
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| Higashi-Oshima Camping Ground |
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| Before
entering parking space for the Camping Ground, we are greeted by rice paddies and farmlands. The water for such agricultural field joins with rainwater dropped on the satoyama forests around, and comes out to Sagami River. |
Basically, unless it is a fish, the aquatic lives along the river use cleverly the continuation of environment from dry forest to water flow. Amphibians often use mass of water only for mating and tadpole-times. They spend most of their adult life in forest. Insects spend their childhood in water but come out of it when they grow up. Even pond skaters or water striders do not use underwater for their mature days. Grasses and aquatic plants are nice places to cling to for larvae, or to use as corridors between dry land and water area. So, when a spring has such vegetation around, it is the place where we focus to hunt for aquatic creatures. Instead of turning up the stones in riverbeds as in Yadoriki Stream 寄沢, this time we shook water bushes above our landing nets and checked what came out.
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| The spring pond we studied |
According to Mr. Hasegawa of Kanagawa Environmental Research Center, the place we waded in the other day was much larger pond before. Now a sandbank that separated the spring pool and the mainstream became much narrower and the main flow Sagami River is approaching to the calm spring well. We may not have a pool next year once a large typhoon comes. Such is the nature of river … Still, in October 2022, the pond was peaceful enough for us to collect waterborne creatures. Inevitably, our net was stuffed by the remnants of plants we shook, and we searched for the animals hiding in a pile of leaves and stems. At first glance, there was nothing, but once we got used to, we started to spot a small movement of something. We caught these creatures by a small spoon or tweezers and threw them into a jar of 80% ethanol for making specimen. They will be examined under the microscope later for exact identification.
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| Beyond the sandbank is the mainstream of Sagami River. |
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| But inside the pool is calm. |
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| Pile of leaves and stems … |
“Please do not throw fishes and amphibians into the ethanol jar. Instead, catch them in a ziplock or small acrylic aquariums filled with river water and aquatic plants. Take photos of them from many angles, and release. Later we identify them from these pictures.” Oh, I see. So, my jar contained several larvae for aquatic insects and lots of lake prawns + pequeño American crawfishes. “Gee … we have to identify these prawns if they are local or invasive species …” “It seems to us the number of American crawfishes are getting larger.” The pros said. Some invasive species are defined by Ministry of Environment as non-desirable creatures in Japanese wilderness. They compete with native kinds for food, or even devour the locals. American crawfishes are making havoc by acting that way in satoyama environment. Finding them at a point where Sagami River enters downstream is not good news. In contrast, from Yadoriki Stream I have never encountered prawns or crawfishes. It would be the case streams running through deep valleys of Tanzawa are still resisting the invasion of non-native species. Yadoriki Stream behaves nicely as water source. Yeah, the spring pool off the Camping Ground has a nicely clear water where fishes swam around our feet, but …
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| Making specimens |
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| The water is coming out from the sand. Could you see it? |
Even though, downstream part of Sagami River is not dominated by uneasy findings. Next week, I show you another place we did for water-monitoring. Our findings were different, I tell you.
1-3-39 Shinomiya, Hiratsuka City, 254-0014
〒254-0014平塚市四之宮1-3-39
Phone: 0463-24-3311
FAX: 0463-24-3300
k-center@k-erc.pref.kanagawa.jp
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