Eucyclogobius newberryi was split into two and the southern portion of its range is now attributed to Eucyclogobius kristinae (Swift et al. 2016).  

This species inhabits mouths of creeks within a restricted range in southern California. Due to pervasive coastal development, its range has been reduced from 13 localities to nine since the 1970s, and has been possibly reduced further to three localities, as it may no longer be viable in six of the known localities. Its estimated extent of occurrence (EOO) is 26 km² and its estimated area of occupancy (AOO) is 20 km². Additional major threats include competition from invasive species and climate change. The population is considered severely fragmented, the number of locations is fewer than 10 (estimated at 3–9 locations), and it is continuing to decline. This species is assessed as Critically Endangered (CR B1ab(i,ii,iii,iv,v)). Some conservation measures are in place, but additional work is needed to prevent extinction.

This species is endemic to southern California, USA, where it has a small and patchy distribution (Swift et al. 2016). Historically, it occurred at 13 localities along a ~60 km stretch of coast from Aliso Creek to Agua Hedionda Lagoon (Swift et al. 2016). Since 1979, it has only been observed at nine localities spanning 29 km from San Mateo Creek to the Santa Luis Rey River and future surveys may confirm a further reduction in range to three nearby localities all occurring on Marine Corps Base Camp Pendleton (Swift et al. 2016). Individuals referred to as Eucyclogobius newberryi collected south of Santa Monica in Los Angeles County are now attributed to this species (Swift et al. 2016). The depth range for this fish is 0–1 m (USFWS 2005).

Based on a minimum convex polygon drawn around the extent of its extant range, the estimated extent of occurrence (EOO) is 26 km². Based on a 2x2 km grid overlaid on the nine extant localities, the estimated area of occupancy (AOO) is 20 km². It is estimated to occur in fewer than 10 locations, based on the pervasive threat from coastal development.

It can be inferred that this species' population size has been actively declining since approximately the 1970s, due to anthropogenic habitat degradation and observed historical decline of number of localities from 13 to nine, which represents a 31% decline since then (Swift et al. 2016). As of December 2015, it has only been observed at three nearby localities all occurring on Marine Corps Base Camp Pendleton at San Onofre Creek, Las Pulgas Creek, and Cockleburr Canyon, and seems to be declining at its largest and most persistent locality at Las Flores in Orange County (Swift et al. 2016). It is believed that this reduced geographic range and population decline is likely a result of its northern and southernmost localities becoming inviable due to anthropogenic modification/habitat destruction (Swift et al. 2016). The population of this species is considered severely fragmented (Swift et al. 2016) as it has limited to no propagule exchange between the creek localities (separated by impassable marine ocean waters and land), and six out of the nine known localities may be unviable.

This species inhabits ponded water environments such as bay-margins and coastal stream-mouth lagoons (Swift et al. 2016). It prefers low salinity, though it can tolerate a variable range (Swift et al. 2016). This species exhibits male choice sexual selection, with females demonstrating colourful display rituals (Swift et al. 2016). Successful females will be granted access to the male's guarded burrow, where the eggs will be laid and fertilized (Swift et al 2016). The maximum standard length is 3.8 cm (Swift et al. 2016).

This species is highly threatened and requires active management to mitigate the immediate danger of extinction (Swift et al. 2016). It has sustained a decline in geographic range of at least 50%, with recent surveys suggesting an even more serious distribution decline (Swift et al. 2016). This decline is caused by both anthropogenic modifications and climate change, making much of this species' historic range inviable, and impacting its ability to recolonize due to its limited dispersal capabilities (Swift et al. 2016). Its low genetic diversity, likely resulting from a small effective population, and both predation and competition from invasive species such as Lepomis cyanellus and Ameiurus melas, further increase this species' risk of extinction in the near future (Swift et al. 2016).

Large jetty structures and marinas constructed at Dana Point and Oceanside during the 1960s and 1970s have degraded portions of this species' habitat, and lead to a more fragmented distribution (Swift et al. 2016). Its northernmost locality, Aliso Creek, has been developed, and its southernmost locality, Agua Hedionda, was converted into a tidal lagoon to facilitate power plant cooling (Swift et al. 2016). Other parts of this species' habitat have been converted to tidal systems as a way to promote restoration and lagoon management, inadvertently disrupting its recovery by negatively altering its preferred environment (Swift et al. 2016). Perhaps the greatest ongoing threat to this species is the desiccation and degradation of its three remaining localities due to increasing drought intensity and the impact of local wildfires on lagoon drainages (Swift et al. 2016, Hulley et al. 2020).

This species is not utilized.

This species has been protected since 2005 under the "Recovery Plan for the Tidewater Goby", enacted by the U.S. Fish and Wildlife Service (Swift et al. 2016). Although it has only been valid since 2016, it was described from specimens of the federally endangered Tidewater Goby, Eucyclogobius newberryi, which has undergone conservation initiates such as artificial reintroduction and habitat preservation (Swift et al. 2016).

Swift et al. (2016) states that in order to prevent extinction, individuals of this species should be introduced to additional localities, and recommends that captive populations be maintained.