Water Quality and Algal Data for the North Umpqua River Basin, Oregon, 2005

The upper North Umpqua River Basin has experienced a variety of water-quality
problems since at least the early 1990's. Several reaches of the North Umpqua
River are listed as water-quality limited under section 303(d) of the Clean
Water Act. Diamond Lake, a eutrophic lake that is an important source of water
and nutrients to the upper North Umpqua River, is also listed as a
water-quality limited waterbody (pH, nuisance algae). A draft Total Maximum
Daily Load (TMDL) was proposed for various parameters and is expected to be
adopted in full in 2006.

Diamond Lake has supported potentially toxic blue-green algae blooms since 2001
that have resulted in closures to recreational water contact and impacts to the
local economy. Increased populations of the invasive tui chub fish are
reportedly responsible, because they feed on zooplankton that would otherwise
control the algal blooms. The Final Environmental Impact Statement (FEIS) for
the Diamond Lake Restoration Project advocates reduced fish biomass in Diamond
Lake in 2006 as the preferred alternative. A restoration project scheduled to
reduce fish biomass for the lake includes a significant water-level drawdown
that began in January 2006. After the drawdown of Diamond Lake, the fish
toxicant rotenone was applied to eradicate the tui chub. The lake will be
refilled and restocked with game fish in 2007.

Winter exports of nutrients from Diamond Lake during the restoration project
could affect the summer trophic status of the North Umpqua River if retention
and recycling in Lemolo Lake are significant. The FEIS includes comprehensive
monitoring to assess the water quality of the restored Diamond Lake and the
effects of that restoration downstream. One component of the monitoring is the
collection of baseline data, in order to observe changes in the river's water
quality and algal conditions resulting from the restoration of Diamond Lake.
During July 2005, the USGS, in cooperation with Douglas County, performed a
synoptic survey of water quality and algal conditions, the results of which can
be used for comparison with post-restoration conditions in the river as well as
with those documented in an earlier study in 1995. This report presents data
from that survey.

[Summary provided by the USGS.]