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Lake Merwin is located 9.75 miles northeast of Woodland. It is an artificial reservoir in the north fork of the Lewis River below Yale Reservoir. It is 12 miles long, with 2,400 acres in Clark County, and 1,690 acres in Cowlitz County. In addition to receiving water from the north fork of the Lewis River, it is fed by Speelyai, Brooks, Rock, Canyon, Buncombe Hollow, Indian George, Jim, Cape Horn, and Marble Creeks. Lake Merwin was monitored by Ecology staff only.
Size (acres) 4000 Maximum Depth (feet) 190 Mean Depth (feet) 104 Lake Volume (acre-feet) 416000 Drainage Area (square miles) 730.00 Altitude (feet) 239 Shoreline Length (miles) 32.0
Source of morphometric data: Water Supply Bulletins 42, 43, and 57.
VOLUNTEER-COLLECTED SECCHI DATA ________________________________________________________________________________________________________________________ Date Temperature Water %Cloud Recent Secchi Lake (Y/M/D) (C) (F) pH Color Cover Rain Wind (ft) Ht(in) Abbrev. Comments ________________________________________________________________________________________________________________________ STATION 1 95/05/29 Mod Green 0 16.3 0.0 FIELD VISIT ________________________________________________________________________________________________________________________
LABORATORY RESULTS ________________________________________________________________________________________________________________________ Total Total Fecal Col. Bacteria Turb- Suspended Solids Phosphorus Nitrogen Chlorophyll (colonies/100 mL) idity Total Non-Volatile Color Date Strata (ug/L) (mg/L) (ug/L) Site 1 Site 2 (NTU) (mg/L) (mg/L) (Pt-Co) ________________________________________________________________________________________________________________________ STATION 1 95/05/29 E 11 0.07 1.7 1.4 95/05/29 H 8 0.02 ________________________________________________________________________________________________________________________ E=epilimnion composite, H=hypolimnion composite. Remarks codes: U = Below detection limits; J = Estimate.
SUMMARY OF VOLUNTEER SURVEY There was no survey response for 1995. FIELD OBSERVATIONS OF ECOLOGY STAFF There is heavy recreational use with lots of motorboats. There is some floating woody debris.
TROPHIC STATUS Estimated Trophic State: Oligotrophic Mean Trophic State Index (Secchi): 37N* (Oligotrophic) Mean Trophic State Index (Total Phosphorus): 39S* (Oligo-mesotrophic) Mean Trophic State Index (Chlorophyll a): 36 (Oligotrophic) *The calculated TSI is an estimate. The Secchi disk hit bottom (B), entered the weeds (W), or there were too few valid readings (N), or the calculation was based on qualified data (J), or TSIP was based on spring data (S).
SUMMARY AND EXPLANATION OF TROPHIC STATE ASSESSMENT Lake Merwin was not sampled in the summer so summer time phosphorus data is unavailable for TSI analysis. Secchi and chlorophyll data are very close in their estimation of TSI, both indicative of an oligotrophic lake. Spring time dissolved oxygen concentrations are quite high in the hypolimnion which is also indicative of an oligotrophic lake. Therefore, Lake Merwin is classified as oligotrophic.
COMMENTS FROM 93/08/30 AQUATIC PLANT SURVEY Aquatic plants were surveyed at the public access and at one to three transects around the lake. A thorough survey was not made and the list below may be incomplete.
AQUATIC PLANT LIST (This list may be from multiple years and sources.) Nitella or Chara Potamogeton sp (thin leaved) or Heteranthera dubia (thin leaved pondweed-like)
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