River basins of Italy.

Italy’s mountainous geography and glacial past created a network of distinct river basins, each with its own trout lineages and aquatic character.
From the cold marble-trout rivers of the Alps to the isolated Mediterranean streams of Sicily and Sardinia, these basins represent the foundation of Italy’s native salmonid diversity.

Northern Adriatic basin.

The Northern Adriatic system includes the Po River basin and all Alpine rivers flowing east and south to the Adriatic Sea, from the Adda in the west to the Isonzo (Soča) in the east.
It is the heartland of Italy’s cold-water fisheries and the stronghold of the marble trout.

Key Species:

• Marble Trout (Salmo marmoratus) — native and protected.
• Adriatic Grayling (Thymallus aeliani) — survives only in a few tributaries of the upper Po basin; Probably extinct elsewhere.
  
• Alpine Charr (Salvelinus umbla) — native to deep alpine and subalpine lakes (Como, Garda, Maggiore, Iseo).
  
• Lake Garda Trout (Salmo carpio) — endemic to Lake Garda, one of Europe’s few deep-water lake trout.
  

Major Rivers (basin):

• Soča River basin.(Isonzo.)
• Po River Basin.
• Adige River basin.
• Brenta River basin.
• Piave River basin.
• Tagliamento River basin.

Danube River basin.

A small area of Italy’s far north drains into the Danube system, linking Italian waters to the Black Sea.
These include the Inn River headwaters around Lago di Livigno and minor tributaries of the Drava and Gail near the Austrian and Slovenian borders.

Key Species:

• Brown Trout 'Danubian' (Salmo trutta) — native and widely distributed.

Apennines. (Adriatic side)

Rivers draining the eastern slopes of the Apennines flow through limestone and karst landscapes toward the Adriatic Sea.From Emilia-Romagna south to Abruzzo, they host some of Italy’s most pristine spring-fed trout streams.

Key Species:

• Mediterranean Trout (Salmo ghigii) — dominant native species, locally adapted to each drainage.

Major Rivers (basin):

• Metauro.
• Nera.
• Aterno.
• Sangro.
• Tronto.
• Biferno.

Apennines. (Tyrrhenian / Mediterranean side)

Rivers on the western slopes of the Apennines drain toward the Tyrrhenian and Ligurian seas.
They are generally shorter, warmer, and strongly influenced by Mediterranean rainfall patterns.

Key Species:

• Mediterranean Trout (Salmo ghigii) — main native trout across central and southern Italy.
• Lake Fibreno Trout (Salmo fibreni) — endemic to the karstic Lake Posta Fibreno in Lazio.
  

Major Rivers (basin)

• Tiber.
• Arno.
• Volturno.
• Sele.
• Lao.

Sardinia.

Sardinia’s short mountainous rivers and granite valleys hold isolated populations of native trout.
The island’s long separation from the mainland has produced unique genetic signatures within Salmo ghigii.

Key Species:

• Mediterranean Trout (Salmo ghigii) — Sardinian lineage; morphologically distinct, adapted to small, steep streams.
  

Sicily.

Sicily’s rivers host two distinct native trout lineages.
The southern and eastern basins hold Salmo cettii, while the northern rivers flowing from the Nebrodi and Madonie Mountains contain populations of Salmo ghigii, related to the mainland Mediterranean lineage.
Together they form the southernmost native trout populations in Europe.

Key Species:

• Sicilian Trout (Salmo cettii) — endemic and Critically Endangered, restricted to southeastern rivers such as the Anapo, Simeto, and Alcantara.
• Mediterranean Trout (Salmo ghigii) — occurs in northern rivers such as the Tusa, Pollina, and San Leonardo.