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石岡壩魚道，於921地震復建時，為了大甲溪自然生態保育，廣納地方保育團體、學界人士及民意代表之訴求，於右岸壩體受損之16號溢洪道所增設，魚道工程於民國90年4月16日開工，90年12月11日完工。石岡壩魚道係大甲溪繼馬鞍壩後所興建第二座魚道，亦是國內魚道較具規模者，設計水流量0.3立方公尺，其入口(出水口)標高259.57公尺、出口(進水口)標高269.40公尺、總長147公尺，屬於水池階段式(Pool and Step or Pool and Weir Type)，係供洄游生物使用。 依據水利署九十二年三月十三日經水源字第09215002180號函說明二之（三）規定，水庫興建後應持續辦理生態及環境監測，以建立長期性資料庫，並定期辦理水庫興建前後之生態體系變化評估，並配合大甲溪流域整體經理綱要計畫之近中長程目標，在考量生態保育之重要性下，本計畫工作以採集所得的魚蝦類種類與數量，經由豐度、歧異度與均勻度及環境因子相關性等統計分析，以瞭解利用石岡壩魚道的生物種類、利用時機，與石岡壩對洄游生物的影響，並探討有何種生物利用魚道進行洄游，與生物利用魚道的季節，綜合分析石岡壩魚道及其上下游之生態資源狀況。 歷年(截至2020年)石岡壩魚道及其上下游之測站中，記錄10科29種魚類，甲殼類3科5種，水棲昆蟲8目20科，動物性浮游生物7種。魚道內總記錄7科22種魚類，甲殼類3 科4 種。生態調查結果顯示此河段的環境污染低且生物資源相當豐富，紀錄中包含河海洄游的日本鰻鱺、花鰻鱺與對水質較為敏感的臺灣白甲魚等等，也記錄到三級保育類的埔里中華爬岩鰍以及臺灣鮰，另外也有低污染水域的指標生物如扁泥蟲、魚蛉等，若能將魚道功能完善地建立起來，相信會使此河段的水域生態系更加完整。而歷年監測可說明石岡壩魚道的效果良好，本區的水域生態還是維持在相當好的程度，且上下游之間都有非常豐富的河川生物資源。 因此，本計畫進行石岡壩魚道本體及其上下游水域生物監測、歷年水理與水質之蒐集等工作，再經由統計分析及水理分析，以瞭解水域生態資源變化，並探討與魚類生態之間關聯性及上下游生態廊道之通暢性。另提供魚道及其上下水域之生態資源在河道工程施作期間之變化情形。其工作項目包括：(ㄧ)長庚橋至埤豐橋（含魚道）水域生態及洄游生物監測調查、(二)建立石岡壩魚道及其上下游水域生物物種名錄、(三)探討石岡壩魚道及其上下游之水理及水質與水域生物分布關係、(四) 辦理環境教育推廣活動、(五)綜整歷年生態資料與統計分析、(六)評估石岡壩下游在建工程中對於水域生態體系變化的影響及有關生態保育措施、(七)工作報告及成果報告編撰印製等。

The ecological monitoring of fishway and the upper and lower reaches of Shih-Gang Dam was complied on March 8-9, June 14-15, August 30-31, and November 15-16, and two additional investigations of Shih-Gang Dam fishway were complied on April 29 and September 29. The fishway discharge normally during the investigations, and the discharge capacity reach maximum in June due to the huge precipitation the plum rain season. A total of 4,019 fishes in 4 orders, 8 families, 28 species; 304 crustaceans in 1 order, 2 families and 5 species; 4,225 aquatic insects in 7 orders, 24 families; and none of zooplankton were recorded in Shih-Gang Dam fishway and the upper and lower reaches stations. A total of 2,080 fish in 4 orders, 7 families, 22 species and 75 crustaceans in 1 order, 2 families, 5 species were recorded in the six surveys in the fishway. According to the biodiversity indices, there is more biodiversity richness at the upstream of the Chand Gung Bridge and the Pifeng Bridge than others. The possible cause might be that the habitats of the investigation stations mentioned above are more natural. Ecological survey results show that this section of the river has low environmental pollution and abundant biological resources. The records include conservation species like Liobagrus formosanus, Sinogastromyzon puliensis, and migratory species like Anguilla marmorata, as well as the more sensitive to water quality, like Onychostoma barbatulum, Hemimyzon formosanus. It is believed that the ecosystem of this reach will be more complete if the fishway can be fully established in the future. Two batches of environmental education campaign including indoor and outdoor courses were conducted at October 28 and 29. The total attendance of the two batches was 58, and 31 satisfaction questionnaires have been returned. Over 90% of the attendance is satisfied with both the indoor and outdoor courses according to the results of the questionnaires.Comparing with the historical survey in which fish in in 14 families, 47 species and crustaceans in 3 families, 9 species were reported, there isn’t new species added to records in this year: In addition, Onychostoma alticorpus and Spinibarbus hollandi that have been recorded since 107 are invasive species native to the eastern and southern watersheds of Taiwan. According to the record results this year, it can be confirmed that Onychostoma alticorpus and Spinibarbus hollandi have invaded to large scales. The number of the new species of the reach around the Shih-Gang Dam in 2021, Distoechodon compressus, has increased, which mean there is a possibility that this species is intruding the river system, and the considerable number of injured Carassius auratus auratus during the investigations in March and April indicates that there might be animal release around the Shih-Gang Dam. Besides, there is new record of Rhinogobius rubromaculatus and Puntius snyderi at the upstream of the Chand Gung BridgeThe downstream of Shih-Gang Dam is under the river stability and energy dissipation improvement construction, and the main construction area is between the right bank of the energy dissipation pool and the downstream of the auxiliary dam during 2022. Several conservation measures are employed at the construction area to maintain the fluency of the river, and the abundancy of the aquatic ecosystem. Currently, there isn’t abnormality of environment or living creature found in the construction area.The problems of jet flow of the Shih-Gang Dam fishway exit will affect the efficiency of fresh water creatures to trace upward. There is also a high downstream of the auxiliary dam without ecological corridor facility, which may have a negative impact on ecology. To address the problem, the ecological corridor design has been included in the upcoming energy dissipation dam and groundsill works projects, and it is expected to be improved the situation of the ecology of the reach around the Shih-Gang Dam.