Lake districts—regions with high lake densities—offer valuable opportunities to study how landscape geomorphology shapes both individual and collective lake dynamics. In mountain regions, elevation adds a third dimension to spatial dynamics beyond the two-dimensional patterns typical of lowlands. The Pyrenees, stretching from the Mediterranean to the Atlantic, host numerous lakes formed by glacial erosion during the last ice age. These lakes and ponds are largely isolated from the surrounding lowlands, where standing water is rarer, and the climate is drier and more Mediterranean. The LacusPyr dataset provides a comprehensive, georeferenced catalog of Pyrenean lakes and ponds, along with basic geomorphological information relevant to limnological research and conservation (e.g., lake elevation, lake area, watershed area, depth, perimeter). The dataset is designed to be updated and expanded over time, ensuring its continued usefulness for environmental scientists studying Pyrenean lake systems.

Lake information

MiraMon (Pons 2022) and QGIS (QGIS Development Team 2022) were used as GIS software for most tasks. Lake polygons were compiled from several sources. The EMERGE dataset (Catalan et al. 2009) consisted of a catalogue of natural lakes > 0.5 ha in the Pyrenees, which was expanded with Catalan Pyrenean lakes and ponds within the Lacustrine Systems of Catalonia, Catalan Water Agency (ACA) project. These polygons were manually digitized in the year 2000 using the existing highest-resolution maps available as a reference for the lakes from France, Andorra, and Aragon (western Spanish Pyrenees), while lakes and ponds from Catalonia (eastern Spanish Pyrenees) were obtained from the first digital cartographic maps of the Institut Cartogràfic i Geològic de Catalunya (ICGC). The initial catalogue was further developed in the present dataset to include smaller lakes and ponds within an expanded study area (approximately 100 km from the ridgeline on each side of the range), using water bodies polygons of the Spanish cartography BCN25 (Instituto Geográfico Nacional 2015) and the French cartography BD TOPO ® v. 2.1 (Institut national de l'information géographique et forestière (IGN-F) 2015), the last dataset being used only for a validation process of the manually delineated ones. Both databases contained layers or attributes that allowed the classification of lakes as natural or artificial. Natural lake polygons were selected for subsequent analysis.

The provided geographic coordinates correspond to the geometric centre of each lake. Lake elevation was derived from the mean elevation of the lake polygon in the Aster Global Digital Elevation Model Map v3 (NASA/METI/AIST/Japan Spacesystems and U.S./Japan ASTER Science Team 2019), with a ~30 m spatial resolution. Averaging elevation values across the polygon was particularly useful for smaller lakes and ponds, where the DEM’s spatial resolution resulted in limited pixel coverage over open water.

Lake area and perimeter were obtained from the geometric information stored in the vectorial “.pol” files. These files are topologically structured in the MiraMon GIS environment, ensuring consistent geometric calculations.

The watershed polygons for each lake were generated in GRASS GIS v. 7.0.4 (GRASS Development Team 2016). Lake catchments were automatically delineated using the “r.stream.basins” module, which derives drainage basins from a flow-direction grid and an individual lake raster. The polygon areas were included in the final database table. The DEM's precision and resolution constrained the applied automatic process.

Maximum and mean depths were collated from the literature (Gaurier 1934; del Castillo Jurado 1992) and from the research group surveys, mostly from EMERGE, and LIFE LIMNOPIRINEUS / LIFE RESQUE ALPYR projects, among others. When only maximum depth is indicated, it implies that it was estimated from simple transects rather than from a proper bathymetry. Mean depth annotations imply the availability of adequate volume estimates relative to the lake area.

Lake names were compiled from several documentary sources. They are provided to facilitate communication, but not as rigorous geographical identifiers due to historical variability. Due to the different languages historically used across the Pyrenees (and that generated the names of the lakes: Aragonese, Catalan, French, Occitan including the different dialects such as Aranese, still spoken in the Aran valley), historical contingencies, and varying levels of academic and administrative knowledge of the mountain range's detailed toponomy, many lakes may appear under different names or spellings in cartographies and studies. In some cases, toponyms remain a matter of debate. Concerned by the multiplicity of names for the same location in the literature, we have developed a file of lake names, including those that are not currently official, linked by the LacusPyr code. The list is considered an open inventory that can be regularly updated with ancient names used in the limnological literature or with newly officialized toponymic updates. Ultimately, the aim is to enable lake references appearing in past or future limnological studies to be cross-referenced with the least ambiguity possible.

Technical Validation

In general, there was a high degree of concordance between the cartographic sources used and the DEM modelling. Disagreements between sources or field observations during limnological studies in the area conducted by the groups involved in developing the catalogue were resolved through individual analyses of each case. The distinction between shallow lakes and wetlands, or wide stream parts, in plains was difficult to resolve in some cases, since ancillary data or field observations indicated that some delineated lake polygons could correspond to these other typologies. When it was possible to distinguish false positives using orthophotos, they were removed from the inventory. Another circumstance that required specific judgment was the presence of water bodies in wide, gently sloping cirque valleys, where there are no significant elevation differences among adjacent lake basins. During high water levels, for instance, during the thawing period, some may appear as single water bodies that break into several isolated pieces when the water level drops during drier periods. There is no consistent treatment of these cases in the cartography. Future use of the information and field evaluation will sort out the ambiguities. Finally, recent glacial retreat across the Pyrenees is unveiling new cirque lakes (Serrano 2022), some of which are not yet included in the available cartography. Field observations and Google Earth images were used to identify some of them.

A manual review of water bodies labelled as natural below 1800 m a.s.l. was conducted, given that fully artificial water bodies were more common at lower elevations. Some polygons were reclassified from natural to artificial after visual inspection using Google Earth orthophotos.

Watersheds delineated by an automated process may be affected by the DEM's spatial resolution and local drainage artefacts. For the EMERGE dataset lakes, watershed areas were also available as manually delineated polygons from paper maps, occasionally at a different scale. The vast majority of lakes showed rather similar watershed areas for the automatic and the former manual procedure. For cases with conspicuous discrepancies between the two methods, we manually reviewed each case, revised the watershed polygon, and assigned the corresponding new area. Furthermore, we reviewed other cases and manually corrected them when the watershed delineation was suspected to be inaccurate by visual inspection (e.g., rivers crossing watershed boundaries).

Some high-mountain lake areas of the Pyrenees were deeply affected by hydroelectric power generation over the 20^th century, usually aimed at concentrating the hydrological potential of several cirque watersheds in a single valley power station. The variety of interventions is large including small dams in medium-size lakes, which barely modified the lake area and volume; large subterranean excavations enhancing the connection between relatively large lakes, sometimes from watersheds not naturally connected; a few large dams that completely modified the water body, becoming another type of ecosystem; and, finally, built more recently, some large lakes are reversibly connected to down valley new built reservoirs for pumping up energy excedents when suitable. A detailed inventory of these modifications has been performed for some areas (Catalan et al. 1997), but a systematic gathering and collation of information is pending for the whole lake district. In LacusPyr, the lake areas correspond to the current situation; however, the lake watersheds do not account for subterranean connections among lakes, nor for potential horizontal deviations towards down-valley power stations, which eventually reduce the water flow to lakes downhill in the same valley. For specific studies on highly affected lakes, the current effective watershed should be further evaluated.

The catalogue and information are planned to be updated and expanded in future versions to remain a useful tool for limnologists and other environmental scientists interested in the Pyrenean lakes and their conservation.  

References

Catalan, J., C. J. Curtis, and M. Kernan. 2009b. Remote European mountain lake ecosystems: regionalisation and ecological status. Freshw Biol 54: 2419-2432. https://doi.org/10.1111/j.1365-2427.2009.02326.x

Catalan, J. and others 1997. The hydraulic industry in the Pyrenees: evaluation, correction and prevention of the environmental impact at the Aigüestortes i estany de Sant Maurici National Park (In Catalan). La Caixa.

del Castillo Jurado, M. 1992. Morfometría de lagos. Una aplicación a los lagos del Pirineo. .  Universitat de Barcelona.

Gaurier, L. 1934. Les lacs des Pyrénées françaises. Commentaire de l'atlas couronné par l'Académie de Sciences.

Pons, X. 2022. MiraMon: geographic information system and remote sensing software. Centre de Recerca Ecològica i Aplicacions Forestals (CREAF). Bellaterra, Spain. URL: https://www.miramon.cat.

QGIS Development Team. 2022. QGIS Geographic Information System. Open Source Geospatial Foundation. URL: https://qgis.org.

Serrano, E. 2022. The existing glaciers of the Iberian Peninsula, p. 525-553. In M. Oliva, D. Palacios and J. M. Fernández-Fernández [eds.], Iberia, land of glaciers. Elsevier.