The semiaxes are: 3.2/2 = 1.6 ft long vertical and 6.3/2 = 3.15 ft horizontal.


So, the standard form equation for this ellipse is

     +  = 1,


written with the center of the ellipse as the beginning of coordinates.


The level of water is at y = -1.6 + 0.85 = -0.75 ft.


Substitute this value of y into the ellipse equation

     +  = 1,

and get

     = 1 - 

or

     = 0.780273438.


It implies

     =  = 7.742263189,

    x =  = 2.782492262.


So, the water surface is from x= -2.782492262  to  x= 2.782492262
.


Thus the wide of the stream is  2*2.782492262 = 5.564984524 ft,  or 5.565 ft  (rounded).


ANSWER.  The width of the stream is 5.565 ft,  rounded.