the outlet was flowing at that time. By March all flow in the pit had ceased 

 and the pit and outlet were frozen to the bottom. The spring-fed tributary, 

 Willow Creek, however, remained open and flowing into March, but fish were 

 not detected either in the tributary or in the Penny River downstream from 

 where the tributary entered the mined area. At West Fork Tolovana River, the 

 outlet was blocked at the time of the first winter visit, 29 November 1979, 

 because the deep, low velocity arm connecting the pit to the river was 

 frozen and the other arm flowed through a beaver dam. Flow out of the pit 

 through the beaver dam persisted through March (Figure 59). Fish were not 

 detected during any of the winter visits. There was sufficient water and 

 dissolved oxygen to support overwintering fish in mid-March 1979 and the 

 persisting outflow through the beaver dam indicates the pit may be receiving 

 some intergravel flow from the river. 



The Tanana River-Downstream pit was visited only on 6-7 March 1979; 

 fish were not captured but as emigration after the previous September visit 

 was not possible, fish were probably present. The dissolved oxygen should 

 not have been depleted because of the depth, limited phy top I ank ton pro- 

 duction, and absence of littoral vegetation, and, in fact, was 6.0 mg/d- in 

 March (Table 24). At the two Tanana R i ver-Upstream pits, a more dynamic 

 pattern of freezing was observed. On 27-28 November 1978, the connection 

 between the two pits was frozen solid, thus isolating the upper pit. The 

 surface of the ice in the upper pit was approximately 1.5 m higher than the 

 surface of the lower pit. A burbot and possible lamprey were observed with 

 an underwater television system. The outlet of the lower pit was open to the 

 Tanana River with a school of juvenile salmon and two species of whitefish 

 holding in the outlet current. Burbot were captured by setline in the lower 

 pit. On 6-7 March 1979, the ice surface of the lower pit had risen to the 

 level of the upper pit and the connection between the two pits was open, 

 approximately 30 cm deep and flowing at about 0.1 m/sec into the lower pit. 

 The outlet to the lower pit was frozen solid. Dissolved oxygen at the upper 

 pit had increased from 3.4 to 6.0 ppm between November and March. Fish were 

 not detected in either pit in March. 



195 



