# Mouly hydroelectric plant Publisher: CapexCue Canonical dossier: Dossier reference: release 1 (67397306-db5a-4f84-ab19-41bef1a4f18c) Released project intelligence Oldest supporting observation: 2026-10-03T05:19:19.751882+00:00 Dossier released: 2026-10-16T06:54:01.636706+00:00 Source report dates and capture dates are listed per fact below; neither establishes an event date. Original released project name: Mouly hydroelectric plant, also known as the Pont des Grottes plant. ## Project summary The Mouly hydroelectric plant, also called the Pont des Grottes plant, is an existing run-of-river facility on the Gave de Pau at Lestelle-Bétharram and Saint-Pé-de-Bigorre. SARL de Lauture is identified as its operator and project proponent. The proposal would expand the headrace, add a new powerhouse and turbine, and rework the weir to provide fish and boat passages. Proposed maximum gross power is 597 kW; the opinion reports 2,423 MWh/year as the proponent’s more realistic modeled generation estimate, distinct from a theoretical 2,610 MWh calculation. The environmental authority’s opinion, dated 25 September 2025, raises concerns about ecological continuity, habitats, climate-related flows and sharing water with whitewater recreation. It calls for stronger analysis of hydrology and impacts. The opinion is neither favorable nor unfavorable and is not an authorization decision. ## Evidence limits and unknowns - Whether the environmental authorization or other required permits were granted after the 25 September 2025 opinion, and whether public participation subsequently took place. - Construction start dates and the final confirmed works schedule. The opinion describes two planned six-month phases during low-water periods but says the file does not clearly explain the works, duration or sequencing. - Final detailed drawings and exact boundaries of excavation, infill, canal widening and work around the existing powerhouse; the opinion says these descriptions were incomplete. - The final operating and reserved-flow regime, including how it will address future hydrological conditions and balance ecological needs, electricity generation and water sports. - Project financing, named contractors, procurement arrangements and the identity of the electricity purchaser are not established in the supplied extracts. - The supplied text covers pages 2–12 and 27–28 of the 28-page opinion; pages 13–26 and graphical content were not interpreted. Current purchasing availability: unknown. Source-dated plans do not establish current progress or available supplier packages. ## Project metadata Country: France Region: Europe Physical assets: Hydropower Derived from the exact released evidence; unresolved fields remain unclassified. ## Project category Energy Derived from the reviewed scope statement; delivery stage remains unclassified. The existing run-of-river installation is described as having a roughly 415 m headrace canal, a Kaplan turbine in the existing powerhouse, a 16 m tailrace, and a weir; its reported baseline is 149 kW maximum gross power and about 780 MWh/year average generation over the preceding 18 years. The integrated proposal would widen and extend the headrace along its left bank, install a new turbine in a new powerhouse while retaining the existing building and recycling its equipment, replace the headgate, and rework the existing weir to add a fish pass and rebuild the boat passage. The new powerhouse is not to have a fish pass. About 11,300 m³ of excavated earth is to be made available to neighboring agricultural landowners. The proposed maximum turbine flow is 14 m³/s from November through May and 6.9 m³/s for the rest of the year; proposed maximum gross power is 597 kW. The opinion reports modeled annual generation of 2,423 MWh as the proponent’s more realistic estimate, while also noting a theoretical calculation of 2,610 MWh. The opinion says the currently authorized maximum diverted flow is 3.5 m³/s but that actual diversion is about 6.5 m³/s, reported in the file and confirmed during the exchange with the reviewers. It describes a current reserved flow of 10 m³/s. Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 Project overview Oldest decisive evidence: 2026-10-03T05:19:19.751882+00:00 Newest evidence: 2026-10-03T05:19:19.751882+00:00 Knowledge reviewed: 2026-10-16T06:54:00.044319+00:00 Publication reviewed: 2026-10-16T06:54:00.044319+00:00 ## Name Mouly hydroelectric plant, also known as the Pont des Grottes plant. Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Scope The existing run-of-river installation is described as having a roughly 415 m headrace canal, a Kaplan turbine in the existing powerhouse, a 16 m tailrace, and a weir; its reported baseline is 149 kW maximum gross power and about 780 MWh/year average generation over the preceding 18 years. The integrated proposal would widen and extend the headrace along its left bank, install a new turbine in a new powerhouse while retaining the existing building and recycling its equipment, replace the headgate, and rework the existing weir to add a fish pass and rebuild the boat passage. The new powerhouse is not to have a fish pass. About 11,300 m³ of excavated earth is to be made available to neighboring agricultural landowners. The proposed maximum turbine flow is 14 m³/s from November through May and 6.9 m³/s for the rest of the year; proposed maximum gross power is 597 kW. The opinion reports modeled annual generation of 2,423 MWh as the proponent’s more realistic estimate, while also noting a theoretical calculation of 2,610 MWh. The opinion says the currently authorized maximum diverted flow is 3.5 m³/s but that actual diversion is about 6.5 m³/s, reported in the file and confirmed during the exchange with the reviewers. It describes a current reserved flow of 10 m³/s. Status: planned Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Country France Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Ecology The opinion identifies ecological continuity, aquatic and alluvial habitats, water quality, climate-related changes to flows, and sharing water with whitewater recreation as important issues. It identifies the Atlantic salmon, European otter and Pyrenean desman among relevant species; the existing structures are described as preventing fish passage, and the proposed fish pass is intended to address this. The opinion raises concerns that the assessment does not adequately establish how the project will protect habitats and reconcile water uses under changing flows, and calls for better baseline and impact analysis. It also reports a sharp decline in observed salmon reproduction in 2024 and a fishing prohibition effective from July 2024. A monitoring program is described, including flow monitoring, fish surveys and reporting, but the opinion notes that monitoring frequencies, alert thresholds, responsibilities, resources and reporting arrangements are not adequately specified. Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Activity The existing facility generates hydroelectricity. The same river reach is also used for whitewater recreation and training, including slalom and freestyle kayaking; the opinion describes the site as a rare natural kayaking site in France and notes international-level practice on this stretch. Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Delivery The works were described during the reviewers’ site visit as planned in two phases of six months each, scheduled for low-water periods. The opinion says the file does not clearly or consistently explain the works, their duration or sequencing. Described operations include dewatering the headrace for construction of the new powerhouse, followed by staged dewatering at the weir to widen the canal, install gates and repair the intake, then construct the fish pass and boat passage. Status: planned Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Location On the Gave de Pau, across Lestelle-Bétharram in Pyrénées-Atlantiques (department 64) and Saint-Pé-de-Bigorre in Hautes-Pyrénées (department 65), spanning Nouvelle-Aquitaine and Occitanie. The opinion notes administrative complexity, including differing status of the banks. Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Developer SARL de Lauture is identified as the current operator and as the project petitioner/proponent. Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Regulatory The environmental authority issued its opinion on 25 September 2025 after receiving the file on 15 July 2025. The opinion is neither favorable nor unfavorable and is not the authorization decision. The project is subject to environmental assessment following case-by-case review; the proponent submitted an environmental impact study voluntarily, and the described environmental authorization application also covers water-law and electricity-generation authorizations. The project is subject to Natura 2000 impact assessment. The opinion says the existing installation had not completed all compliance works prescribed in 2003 and lacked a water operating regulation. It also notes an earlier environmental opinion in 2016 and references to a public inquiry initially planned for 2017, whose status required clarification following regulatory changes. The supplied material does not establish whether the current application has since been authorized or whether a public inquiry has occurred. Status: reported Attribution: IGEDD Autorité environnementale opinion: authority synthesis and attributed developer facts Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/3_-_centrale_hydroelectrique_du_mouly_sur_le_gave_de_pau_cle1f9fef.pdf | published unknown | observed 2026-10-03T05:19:19.751882+00:00 ## Cite this dossier CapexCue — Mouly hydroelectric plant — dossier released 2026-10-16T06:54:01.636706+00:00, release 1 (67397306-db5a-4f84-ab19-41bef1a4f18c) — https://capexcue.com/projects/mouly-hydroelectric-plant-also-known-as-the-pont-des-grottes-plant-7699ab5f50c00b9a/. For current information and later dossier updates, visit . This file records the release identified above; the current dossier may change.