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TOP > Sightseeing Highlights> Kiryu Area Nature Guide> Watarase River
| The Watarase River runs down from the mountains in the Ashio area and, at the town of Omama, flows into the Kanto Plain. Here the river widens and its current slackens. As it continues on southwesterly, there is a twelve mile stretch where it passes through the city of Kiryu from Aioi to Hirosawa. Both the Yamada and Kiryu rivers are tributaries of the Watarase River. Fish abound in the river. Among the many varieties, there are freshwater minnows1(oikawa), dace2 (ugui) and sweetfish3 (ayu). There are many large and small rocks lying about the banks of the river and on the riverbed. The majority of these igneous rocks include: andesite, granite and quartz porphyry. In addition, sedimentary rocks such as chert and slate can also be found. The majority of the households in Kiryu draw their drinking water from the Watarase River. 1Zacco platypus 2Tribolodon hakonensis 3Plecoglossus altivelis |
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| PUBLIC PARK AREA (shimin hiroba) The people of Kiryu enjoy taking their families to the Public Park on Sundays. There are many large rocks and boulders in this area. The river current here is quite swift. It is a good location to observe the winding course of the river, the erosion which has occurred along the riverbanks, and the layers of stratified rock exposed on either side of the river. Notice how the size and location of the boulders and rocks vary depending on whether they lie on the inside or outside of the bend of the river. Crossing over Akaiwabashi toward downtown Kiryu, there is an immense outcropping of chert, a very hard rock. Because chert is so hard, the force of the current has not worn down the rock and it remains exposed in the riverbed. |
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| Plant Life Proceeding from the Public Park area toward the river, a large black locust tree1 (niseakashia) can be found growing there. Locust trees are often found along riverbanks or in wilderness areas. In early May the tree is covered with fragrant white blossoms. Along the riverbank Japanese reeds2 (tsuruyoshi) and common reeds3 (ogi) along with other grasses are growing in abundance. In some places, pussywillows4 (nekoyanagi), Hakuro Nishiki willows5 (inukoriyanagi), and the quince-leaved willow6 (akameyanagi) can also be found. Because of dramatic changes in temperature and humidity along the river, it is not a very conducive environment for plants. In particular, the surface of the ground in summer can sometimes approach 60 degrees centigrade. For this reason, the variety of plants which can survive along the river is limited. Japanese reeds are representative of the type of plant life commonly found near the river. Mugwort7 (yomogi) and wormseed8 (kearitaso), and other wild plants can be found as well. Where the water ripples by you will often find knotweed9 (mizosoba) growing, and where the woods are close to the embankment, rough hedge parsley10 (oyabujirami) grows well. Rough hedge parsley is a member of the dropwort family and is a favorite source of food for the yellow swallowtail butterfly11 (kiagehacho). 1Robinia pseudoacacia L. 2Pragmites japonica Steud. 3 Miscanthus sacchariflorus Benth. 4Salix gracilistyla Miq. 5Salix integra Thunb. 6Salix chaenomeloides Kimura 7Artemisia princeps Pampan. 8Chenopodium ambrosioides L. 9Polygonum thunbergii Sieb. et Zucc. 10Torilis japonica DC 11Papilio machaon hippocrates C. et R. Felder |
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| Animal Life Looking closely at the leaves of the Japanese reed, you will notice that some may have been bent to form a nest. This is the nest of a foliage spider1 (kabakikomachigumo). A spider bite from this species is particularly painful and should be avoided at all costs. The Japanese great tit2 (shijukara), brown-eared bulbul3 (hiyodori) and gray starling4 (mukudori) live in these woods year round. In winter, you can see the Daurian redstart5 (jobitaki) and dusky thrush6 (tsugumi), and in summer, the gray thrush7 (kurotsugumi) and stonechat8 (nobitaki). Fantailed warblers9 (sekka) build their nests in the rushes that grow along the riverbed during spring and summer. This bird is a relative of the bush warbler10 (uguisu) and looks very similar to the sparrow (suzume). They are, however, slightly smaller than sparrows and are somewhat whiter in appearance. During the breeding season in June, male fantail warblers circle over their territory crying out, "hee, hee, hee" in ascending scale. And when returning to their nest, they cry out "cha cha cha" as though they were a totally different species of bird. Next to the parking lot at the Public Park there is a stand of sawtooth oak trees, most of which are approximately 20 cm in diameter. In summer both saw stag beetles11 (nokogirikuwagata) and rhinoceros beetles12 (kabutomushi) are attracted to these trees and their offspring can be seen burrowing into the roots of the trees. 1Chiracanthium japonicum Boes. et Str. 2Paris major 3Hypsipetes amaurotis 4Stumus cineraceus 5Phoenicurus auroreus 6Turdus naumanni 7Turdus cardis 8Saxicola torquata 9Cisticola juncidis 10Cettia diphone 11Prosopocoilus inclinatus 12Allomyrina dichotoma septentrionalis |
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| Kin'obashi Bridge Vicinity The river widens out in the Kin'obashi Bridge area. Some of the flat areas along the riverbed have been developed into sports and recreation fields. Many people enjoy playing baseball and soccer here. Cement has been laid along portions of the embankment by riverbank protection projects making it impossible to observe the riverside in its natural state, however, along the course of the river many of the original rocks and boulders can be found. Igneous rocks found in the river include granite, andesite, quartz porphyry, and rhyolite. Sedimentary rocks include chert and slate, etc. The Watarase River flows down from the mountains around the town of Ashio. Local geological studies indicate that the rocks were formed during the Paleo- and Mesozoic Eras and are predominantly chert and slate in composition. During these same eras, magma, slowly erupting from deep within the earth, cooled and hardened to form granite. There is much granite along the river in the Kusaki Dam area and it is currently being quarried there. Jizodake on Mt. Akagi is composed of quartz porphyry and rhyolite. Koshinzan is composed of andesite. The rocks and boulders along the headwaters of the Watarase were cut during great floods and over immense periods of time. Eventually, they found their way into the riverbed. |
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| Plant Life Much of the riverside is covered in reeds and Jerusalem artichokes1 (kikuimo). Jerusalem artichokes are originally from North America and have become naturalized plants. They were cultivated for their root vegetables, but because they propagate easily, they now grow here and there in the wild. In Japanese they are called &-46kikuimo&-45 because their flowers resemble chrysanthemums (kiku) and the plants yield a potato-like tuber (imo). Other naturalized plants in the area include ragweed2 (butakusa), bouncing bet3 (zabonso), and a wild "Poa" grass4 (ichigotsunagi). Ragweed is well-known for causing hay fever. Recently, other naturalized plants such as common reeds5 (ogi), tall goldenrod6 (seitaka-awadachiso), and the bur cucumber7 (arechiuri), all of which propagate easily, have invaded the native environment and spread rapidly. Near the water&-43s edge, Japanese euptelea8 (fusazakura), Japanese sumac9 (nurude) and the food-wrapper plant10 (akamekashiwa) can be found growing. The fruit and seeds of these trees are carried downstream and propagate along the banks of the river. 1Helianthus tuberosus 2Ambrosia artemisiae 3Saponaria officinalis L. 4Poa spondylodes Trin. 5Miscanthus saccariflorus 6Solidago altissima 7Sicyos angulatus L. 8Euptelea polyandra Sieb. et Zucc. 9Rhus javanica L. 10Mallotus japonicus Muell. Arg. |
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| Animal Life Oriental longheaded locusts1(shoryobatta) and migratory locusts2 (tonosamabatta) abound in the grasses along the river. Gently lifting the rocks you may find a Pardosa type spider3 (kishibe- komorigumo). These insects are present year round. Looking skyward over the water, there may be some blue-gray birds diving into the river. These birds are little terns4 (koajisashi) of the seagull family. These birds gather in flocks and fly over the river in search of food. They are about 25 cm in length, with black heads and white brows. Their beaks are yellow and tipped in black at the end. Little terns migrate to the area in summer, arriving in May, and build nests along the riverbank. You can hear them cry "kee-ree kee-ree" as they fly over the river, diving into it from time to time to catch small fish. Sometime in September they begin their migration to more southerly climes. 1Acrida cinerea antennata 2Locusta migritoria 3Pardosa yaginumai Tanaka 4Sterna albifrons |
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| Matsubarabashi Bridge Area The river gets increasingly wider as it flows south towards Matsubarabashi Bridge. Here the current slackens as well. The rocks seem to have tumbled along and settled in place. They are more or less aligned with the flow of the river. The rocks here are significantly different in size from those found near the Public Park upstream. The rocks near Matsubarabashi Bridge are much smaller and there are more of them. In this area you can see andesite, granite, quartz porphyry, chert, slate, sandstone and Hornfels. The chert here is also different from that located upstream. The rocks are rounder from having tumbled farther downstream, carried along by the current. Chert is hard sedimentary rock composed of fossilized radiolaria from the ocean floor. It is composed of fine material and is slippery to touch. Chert ranges in color from reddish to brown to gray. In times past, chert was used as a flintstone or for stone implements. Slate was formed by the accumulation of clay on the ocean floor. Over the passage of time it hardened into rock. Hornfels is sedimentary slate formed from the action of magma, which, being hot, reformed the slate into a new type of rock. Black stones and rocks speckled in white are colloquially called "sakuraishi" (cherry blossom stones). The proper name for this kind of rock is iolite Hornfels. The white speckling resembles the petals of cherry blossoms, giving the stones an unusual appearance. When polished, these stones make attractive decor. |
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| Plant Life Japanese reeds1 (tsuruyoshi) can be found growing here and there along the riverbed. Like the area near Kin&-43obashi Bridge, ribwort2 (heraobako) and many other naturalized plants abound. Among these, an unusual naturalized plant is the great mullein or velvet plant3 (birodomozuika) from Europe. It has thick leaves, bristling with hairs, and feels very much like velvet. A plant commonly found along the river is riverbank mugwort4 (kawara yomogi). This plant is different from other mugworts in that its leaves are very thin and narrow. This helps to prevent excessive evaporation of moisture, making the plant hardy in dry conditions. 1Phragmites Japonica Steud. 2Plantago lanceolata 3Verbascum thapsus Linn. 4Artemisia capillaris Thunb. |
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| Animal Life Great reed warblers1 (oyoshikiri) can be seen wherever there are reeds growing along the riverbank. These yellowish-brown birds migrate to the area in summer and are a little larger than sparrows. They can be recognized by their loud "gyo-gyoshi, gyo-gyoshi" and "kay-keshi, kay-keshi" cries. Many other varieties of birds can be seen around the Watarase River in summer. These include the spotbill duck2 (karugamo), the Oriental greenfinch3 (kawarahiwa), the little bittern4 (yoshigoi), the little grebe5 (kaitsuburi), the green-backed heron6 (sasagoi), the little egret7 (kosagi), the lesser egret8 (chusagi), the gray wagtail9 (kisekirei), the Japanese wagtail10 (segurosekirei), the barn swallow11 (tsubame), the meadow bunting12 (ho'ojiro), the azure- winged magpie13 (onaga), the kite14 (tobi), the rufous turtledove15 (kijibato), the white- cheeked starling16 (mukudori), the brown-eared bulbul17 (hiyodori), and the skylark18 (hibari). 1Acrocephalus arundinaceous 2Anas poecilorhyncha 3Carduelis sinica 4Ixobrychus sinensis 5Tacybaptus ruficollis 6Butorides striatus 7Egretta garzetta 8Egretta intermedia 9Motacilla cinerea 10Motacilla grandis 11Hirundo rustica 12Emberiza cioides 13Cyanopica cyana 14Milvus migrans 15Streptopelia orientalis 16Sturnus cineraceus 17Hypsipetes amaurotis |
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| Ashio Copper Mine - the Watarase River was an environmental disaster by the end of the 19th century as a result of the runoff from copper mining which caused serious mercury poisoning. The subsequent cleanup of the river is one of the earliest environmental success stories in Japan. Efforts continue to be made to restore the natural environment around the Ashio area and to preserve the now clean waters of the Watarase River. The Watarase River flows into the Tone River, one of the main sources of water for Tokyo. |  |
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