# Lake Bolsena: a crater lake 151 m deep > Lake Bolsena covers 114.5 km2 and is 151 m deep, filling the caldera of the Vulsini volcanoes. It is fifth among Italian lakes and the largest in Lazio. URL: https://myitalia.it/nature/lago-di-bolsena Last updated: 2026-09-11 Lake Bolsena fills an extinct volcanic caldera in Lazio: 114.5 square kilometers of water, 151 meters deep at its deepest, with the surface at 305 meters above sea level. ## The numbers, from two agencies Lake Bolsena has a surface of 114.5 square kilometers, a maximum depth of 151 meters and a shoreline of 43 kilometers, on figures from the Lazio regional water plan confirmed by the regional environment agency. It measures 14 kilometers long and 12 wide, close enough to a circle that the shape reads at a glance on any map. The elevation of 305 meters above sea level appears in only one of the two sources. Treat it as the softer number of the set. ## A crater, not a valley The lake fills the caldera of the Vulsini volcanic complex, and it is the largest lake in the world formed in an extinct volcanic crater, according to the Lazio regional water plan. That world ranking rests on one institutional source, so it's quoted here with its name attached rather than as settled fact. The same plan ranks Bolsena fifth among Italian lakes by area and first in Lazio. The volcanic origin also explains the depth. A valley lake fills a trough carved by ice or rivers; this one fills a hole the ground left when the volcano emptied. ## Two islands, Bisentina and Martana Bolsena has two islands, the Bisentina and the Martana. Boat services to either of them, with their season and their fares, are not in the data verified for this site. Ask at the harbor before counting on a crossing, and don't plan a day around an island visit you haven't confirmed with the operator. ## Bolsena against Trasimeno Trasimeno is larger on the map, at 124 to 128 square kilometers, and ranks fourth in Italy, one place above Bolsena. Depth is where the two part ways. Trasimeno runs 3 to 6 meters deep across its basin, while Bolsena drops to 151 meters: the difference between a lake with a few meters of water in it and a flooded volcano. Trasimeno also has a regional park around it, set up in 1995 over 13,200 hectares. Bolsena's protection status isn't among the verified facts here. See [Lake Trasimeno](/nature/lago-trasimeno) and [Italian lakes by size](/best/lakes-by-size). ## What the numbers leave out Nobody in the sources used here publishes Bolsena's water temperature, bathing quality or boat timetable. Those are the three things a summer visitor asks first, and they're logged as gaps rather than filled with guesses. Check the bathing notices of the lakeside town halls before you swim, and see [Lazio](/regions/lazio) for the rest of the region. ## FAQ ### Is Lake Bolsena a volcanic lake? Yes. It fills the caldera of the Vulsini volcanic complex, and the Lazio regional water plan calls it the largest lake in the world formed in an extinct volcanic crater. That world ranking has a single institutional source behind it. ### How deep is Lake Bolsena? 151 meters at its deepest, over a surface of 114.5 square kilometers and a shoreline of 43 kilometers. Two regional agencies agree on those figures; the surface elevation of 305 meters above sea level comes from only one of them. ### Is Lake Bolsena bigger than Lake Trasimeno? No, Trasimeno is larger at 124 to 128 square kilometers against 114.5, and ranks fourth in Italy to Bolsena's fifth. Bolsena is the far deeper of the two: 151 meters against 3 to 6. ### Can you visit the islands on Lake Bolsena? There are two, the Bisentina and the Martana, but boat services, seasons and fares for them are not among the facts verified here. Ask at the harbor of a lakeside town before you plan a crossing. ## Sources | Fact | Source | Confidence | Valid until | |---|---|---|---| | Il Lago di Bolsena ha una superficie di circa 114,5 km2, una profondita' massima di 151 m e si trova a 305 m s.l.m.; il perimetro e' di 43 km. | [Regione Lazio - Piano di Tutela delle Acque Regionale, BUR n.103 del 20/12/2018](https://www.arpalazio.it/documents/20124/53249/Piano+di+Tutela+delle+Acque+Regionale+-+Aggiornamento.pdf); [ARPA Lazio](https://www.arpalazio.it/ambiente/acqua/laghi) | high | 2030-12-31 | | Il Lago di Bolsena e' il piu' grande lago al mondo formatosi in un cratere vulcanico spento, quinto lago italiano per estensione e il maggiore del Lazio; ospita due isole, la Bisentina e la Martana. | [Regione Lazio - Piano di Tutela delle Acque Regionale, BUR n.103 del 20/12/2018](https://www.arpalazio.it/documents/20124/53249/Piano+di+Tutela+delle+Acque+Regionale+-+Aggiornamento.pdf); [ARPA Lazio](https://www.arpalazio.it/ambiente/acqua/laghi) | medium | 2099-12-31 | | Il Lago Trasimeno ha una superficie dello specchio d'acqua di 124-128 km2 e una profondita' molto ridotta, variabile fra 3 e 6 metri. | [Regione Umbria](https://www.regione.umbria.it/parco-regionale-del-lago-trasimeno); [Regione Umbria - Parco del Lago Trasimeno](https://www.regione.umbria.it/documents/18/2512711/Trasimeno_turismo_giu_15.pdf/754fd253-e5a9-427e-9b1b-2ad66afb126c) | medium | 2028-12-31 | | Il Parco regionale del Lago Trasimeno, istituito nel 1995, si estende su 13.200 ettari in cinque comuni; il lago e' il maggiore dell'Italia peninsulare e il quarto italiano per estensione, con tre isole. | [Regione Umbria](https://www.regione.umbria.it/parco-regionale-del-lago-trasimeno); [Regione Umbria - Parco del Lago Trasimeno](https://www.regione.umbria.it/documents/18/2512711/Trasimeno_turismo_giu_15.pdf/754fd253-e5a9-427e-9b1b-2ad66afb126c) | medium | 2030-12-31 | ## Image https://media.myitalia.it/media/nature.lago-di-bolsena.v2.1600.jpg Author: Ulissevietato.9449. License: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0). Source: https://commons.wikimedia.org/wiki/File:Lago_di_Bolsena_7.jpg ## Other languages - it: https://myitalia.it/it/natura/lago-di-bolsena.md - es: https://myitalia.it/es/naturaleza/lago-di-bolsena.md - fr: https://myitalia.it/fr/nature/lago-di-bolsena.md - de: https://myitalia.it/de/natur/lago-di-bolsena.md