https://www.researchgate.net/publication/228469499_The_marin...
Abstract. The marine otter Lontra felina is an endangered and little-known species living in a fragmented habitat: the coast of Peru and Chile.

Between Chimbote and the limit to Chile, the Peruvian coast encompasses ∼1600 km of about 100 rocky shore patches offering suitable conditions for marine otters alternated by patches of unsuitable habitat (e.g. sandy beaches and/or shoreline without caves).

Interestingly, marine otters have sometimes been observed in rivers, feeding on shrimps in river farms of Camaná and Ocoña (Peru) up to 650 m above sea level (Hvindberg-Hansen 1970; Tello 1972; Viacava et al., 1978; Brownell 1978). There is one report of a marine otter in the Majes River, 40 km away from the ocean (Grimwood 1968).

.... the characteristic heterogeneous alternation of sandy beaches, rocky shores and islands of the littoral compose the habitat of the marine otter (Larivière 1998; Sánchez and Ayala, 2006). They may inhabit islands that are several kilometers offshore. Sánchez and Ayala (2006) reported L. felina on Isla Pescadores (11◦46'S), which is over 6 km away from the mainland but connected by several islets about 2 km away from each other.

Rocky shore patches (Fig. 3) are preferred as they provide protected dens within caves with reproduction and resting places. Caves are above water at high tide and may be exposed to heavy seas (Cabello 1983; Ostfeld et al., 1989; Villegas et al., 2006) and present a variety of architecture (Medina-Vogel et al., 2006). Entrances, which may be several, are often well-defined and do not have a submarine access, as they do have in other otter species (Sielfeld and Castilla, 1999). If sandy ground is present in the inside, nest-shaped cavities may be built (10 cm deep and 50 cm in diameter) (pers. obs. by the author in 2009–2010). Human constructions like wharfs, ship wrecks, boats and artificial caves are used as part of their habitat (Medina-Vogel et al., 2007; Valqui 2004).