414 NATIONAL OCEANOGRAPHIC PROGRAM—1965 
especially in areas where the shores are highly populated. More than 
80 percent of the drift bottles from a single release, made by the Bureau 
in Little Bay de Noc (Lake Michigan), have been returned in a short time. 
Synoptic surveys have been made by the Bureau and other interested groups, 
usually on a cooperative basis. The distribution of temperatures, trans- 
parency, various chemical constituents of the water as determined by these 
surveys, and current measurements made with dye and large floats, have 
been useful in identifying water masses and their movements. The Bureau's 
study in Saginaw Bay (Lake Huron) has demonstrated that oceanographic methods 
for estimating flushing; rates, seaward transport of river waters, and ex- 
change of sea and river waters in marine estuaries, can be used to evaluate 
the circulation of this large freshwater bay. 
Present evidence indicates that the currents in most of the lakes 
are variable and respond rather quickly to wind changes. The synoptic sur- 
veys of Lakes Huron and Michigan describe some large eddies in these lakes 
and some stability in flow patterns that are generated by the flow-through 
in Lake Huron and the outflow of Lake Michigan. The results of our drift 
bottle studies in 1956 indicated no single characteristic current system 
in Lake Huron, although a highly variable west-to-east drift was usually 
present. Surface currents were variable in all of Lake Michigan. A stable 
pattern was not detected during studies in 1954 or 1955. A north-bound 
current was observed several times along the eastern shore. 
The general circulation pattern in all areas of Lake Superior has 
not been studied. Present data show, however, that certain currents per- 
pint. A well defined Littoral current flows from west to cast alon, the 
south shore. This littoral current may be part of a freneral counterclock= 
wise circulation of the entire luke. 
The current svstem of Lake Erie is dominated by the outflow of the 
Detroit River--approximately 180,000 cfs. Circulation in the shallow 
western basin, that receives the flow of the river, is similar in several 
aspects to that of an estuary. River water extends almost to the south 
shore, moves counterclockwise into Pigeon Bay, and flows into the central 
basin through Pelee Passage. A general west to east drift, with at least 
two large eddies, consisting of river water moves along the north shore. 
The main flow apparently is deflected onto the south shore of the eastern 
basin by Long Point. 
Diatoms are the most important constituents of the Great Lakes plank-. 
ton. Zooplankton may occasionally cqual the diatoms in biomass, but not 
in numbers. Blue-reen and »reen algae are especially abundant at times 
in Lake Erie and probably- also. in Lake Ontaxio: Even in Lake Erie, however, 
diatoms uswally comp? i se+/5. percent of the “phvt-on].ankton. The more abundant 
‘diatom genera are Astérionella, CyclotellagFracilaria, . Melosira, Synedra, 
and Tabellaria. Copepods make up the bulk 5f the zooplankton, but proto- 
zoans are more numerous. Cladocerans are very abundant in the summer, and 
rotifers, especially Keratella, are usually plentiful. Cyclops bicuspidatus, 
