input: the northern Lagoon and the heavily developed Benner

Bay Marine basin. Secchi depth reduction was not noted at

Station 11 until five to seven days later and the bottom

was again visible here after another three or four days.

At Stations 1 and 2 more than a week passed before turbidity

reached levels high enough to obscure the bottom. At Sta-

tions 3, 4 and 5 turbidity, while increased, was usually not

severe enough to obscure the bottom.

 The relative transparency of water at various points

is shown in Table 5. These data do not indicate optimum

or usual water clarity because the area was still suffer-

ing some effects of the early May flooding when the measure-

ments were made. In particular, the data from Station 11

greatly underrated the clarity of this water which, under

normal conditions, is probably the best in the whole area.

 It will be noted that the extinction rates given in

Table 5 relate well to the Secchi Depth measured on the

same day (Table 4). If one divides the amount of available

light (surface light) in Table 5 by the extinction rate at

each station, it will be seen that this theoretical limit

of visibility approximates very closely the Secchi Depth

actually recorded. At Stations 2 and 9 these calculated

depths of visibility are greater than the depth to the bottom

(which is visible from the surface at these locations),


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