The biology and ecology of the Tucuxi are strongly related to seasonal variation in water levels (Martin and da Silva 2004, Martin et al. 2004, Gómez-Salazar et al. 2010, Gómez-Salazar et al. 2012b). Tucuxis inhabit all three types of water of the Amazon basin: white water, clear water, and black water. Therefore, physical factors such as visibility and acidity appear not to affect their distribution directly (da Silva and Best, 1996, Leatherwood et al. 2000). They seem to prefer the main channels of rivers and larger lakes where access is not limited by narrow or shallow channels, while rapids and fast-moving turbulent water are avoided. Generally, Tucuxis do not enter flooded forest. They are mostly found within 50 m of the edges of rivers and channels (Martin et al. 2004). Like the sympatric Boto, the Tucuxi shows a distinct preference for junctions of rivers and channels (da Silva and Best 1996, Leatherwood et al. 2000, McGuire 2002, Martin et al. 2004, Faustino and da Silva 2006, Gómez-Salazar et al. 2010, Gómez-Salazar et al. 2012b). The most preferred habitat is where a sediment-rich whitewater channel meets black water of low acidity. The resultant mixing produces highly productive and obviously attractive conditions for dolphins (Martin et al. 2004). The large seasonal fluctuation in river levels (10-16 m) influences the distribution of Tucuxis. They enter lake systems during periods of high water but leave these environments as the waters recede, thus avoiding entrapment (da Silva and Best 1994, Martin and da Silva 2004, Faustino and da Silva 2006, Coimbra et al. 2015). In the Peruvian Amazon, Tucuxis were not found in waters <3m depth in rivers or <1.8 m depth in lakes (McGuire 2002, Leatherwood 1996).

Home ranges and movements of Tucuxis are not known, but individuals may occur in the same area year-round. Two tagged individuals in the Amazon were found within 5 km of the tagging site up to one year later (da Silva and Best 1994). In the Mamirauá area in Brazil, 20 individuals carrying artificial marks were periodically resighted, with one adult male seen in the same locale over a period of nine years (Projeto Boto, unpublished data).

A long-term photo-identification study revealed a maximum known range for individuals of 130 km in Peru's Pacaya-Samiria Reserve (McGuire and Henningsen 2007). According to McGuire (2002), encounter rates were highest in confluences, intermediate in lakes, and lowest in rivers and did not differ among seasons in the latter two. During the dry season, Tucuxis persisted longer in the confluences and occurred in higher densities than in any rainy or intermediate season; the reverse pattern was observed during high water.

Tucuxis occur most often in groups of one to six individuals. Groups of more than nine are rarely observed (da Silva and Best 1994, Martin et al. 2004, Faustino and da Silva 2006, Coimbra et al. 2015, Valle 2017). Vidal et al. (1997) reported overall mean group size of 3.9 in the upper Amazon and Martin et al. (2004) a mean of 2.2 in the central Amazon. Tucuxis were most frequently seen as singles or pairs in rivers and lakes of Peru's Pacaya-Samiria Reserve; seasonal differences in group size were non-significant (McGuire 2002). Surveys in rivers in Colombia, Peru and Ecuador found a large variation in group size, from 1 to 26 individuals, and that group size varied with habitat type, the largest group size being found in confluences (Gómez-Salazar et al. 2012). Group size also varies according to the water level. The composition of groups, however, is unknown.

At least 28 species of mostly small schooling fishes belonging to 11 families are preyed upon by Tucuxis in the Amazon region. The characid family Curimatidae was represented in 52%, Sciaenidae in 39%, and siluriforms in 54% of stomachs analysed (n = 29) (da Silva 1983, da Silva and Best 1994, 1996). During the dry season, fish concentrate in the main water bodies and thus become more vulnerable to predation. During the flood season, many Tucuxi prey species enter the floodplain, making them largely out of reach of Tucuxis (da Silva and Best 1994, 1996).

Tucuxis are found in the Amazon drainage as far inland as southern Peru, eastern Ecuador and southeastern Colombia. They occur in the main tributaries of the Amazon/Solimões River basin, and they cross international boundaries in areas such as Leticia and Iquitos, between Brazil, Colombia, and Peru. The species does not occur in the Beni/Mamoré river basin in Bolivia; nor does it occur in the upper Rio Negro or the Orinoco river basin (da Silva and Best 1996, Caballero et al. 2010a, Caballero et al. 2010b, da Silva et al. 2010, Gómez-Salazar et al. 2012, McGuire 2010).

The main distributional barriers for tucuxis are waterfalls, rapids and shallow waters (da Silva and Best 1996, da Silva et al. 2010). In Brazil, there are no records of the species above the Santo Antônio and Teotônio falls, which are located just above Porto Velho on the Madeira river, nor are there any records from above the falls approximately 200 km from the mouth of the Tapajós River. Tucuxis do not occur above the Belo Monte rapids, which are located below Altamira on the Xingú River, nor do they occur in the Tocantins-Araguaia River basin. The Tocantins river has been cut off from its estuary by the Tucuruí Dam since 1988, although the rapids that were flooded by the reservoir had probably served as a barrier even before the dam’s construction. On the Rio Negro there is a series of rapids beginning at Tapuruquara, about 900 m upstream, while the first major barrier is located 1200 km upstream. There are no records of Tucuxis above the falls of the Trombetas River, the first major one of which is Cachoeira Porteira, which is located about 260 km from the river mouth (da Silva et al. 2010).

In Colombia, Tucuxis do not occur upstream of the Cordoba rapids or upstream of the Estrella and Puerco rapids in the Apaporis river (Caballero et al. 2010a, 2010b). In the Peruvian Amazon, Tucuxis are seen mainly where the rivers are relatively wide and deep and where the current is low (Leatherwood et al. 2000, McGuire 2010). In Ecuador, Tucuxis have been reported in the lacustrine system of the Cuyabeno river (Laguna Grande), at Zancudo and at the mouth of the rivers Cuyabeno and Lagartococha on the Aguarico river, and at the Tiputini river, at lake Jatuncocha and at the Rio Pastaza basin (Zapata-Rios and Utreras 2004).

Tucuxis may move into smaller tributaries during the high-water season, but they do not move into the flooded forest, staying mainly in the main river channels, tributaries and lakes (da Silva and Best 1996, Vidal et al. 1997, Martin and da Silva 2004). Tucuxis are largely sympatric with Botos (Inia geoffrensis) in Amazon River systems (da Silva and Best 1996, Leatherwood et al. 2000, Martin et al. 2004).

The status of Tucuxis has been evaluated using the IUCN Red List Categories and Criteria in several of the range states. Those national assessments classified the species as Vulnerable in Colombia (Trujillo et al. 2006) and Endangered in Ecuador (Tirira 2011). In Brazil, the Tucuxi was classified as Data deficient (DD) until 2008 and it has been classified as Near Threatened (NT) since 2012 (ICMBio/MMA, 2014). In Peru, S. fluviatilis is protected by National Law No. 26585 of April 1996 and the Supreme Decree No.00296-PE of 1996 calls for the protection and conservation of small cetaceans and prohibits the consumption of cetacean meat as well as harassment, disturbance, harm, and injury to the animals (McGuire and Aliaga-Rossel 2010).

Additionally, there is a South American River Dolphins Action Plan (Trujillo et al. 2010a) and national river dolphin action plans for Ecuador (Utreras et al. 2013) and Colombia (Trujillo et al. 2006, Trujillo et al. 2014). In Brazil, the "National Action Plan for the Conservation of Aquatic Mammals – Small cetaceans", was published in 2011 (ICMBio, 2011) and a new Action Plan of the Aquatic Mammals of the Amazon was established  (ICMBio 2019).

In 2020 the governments of Colombia, Brazil, Peru and Ecuador submitted a proposal for a Conservation Management Plan for South American river dolphins to the Scientific Committee of the International Whaling Commission.

The Tucuxi is listed in Appendix I of the Convention on International Trade in Endangered Species and in Appendix II of the Convention on Management of Migratory Species.