The poisoning of Diamond Lake

The picturesque Diamond Lake in the Umpqua National Forest in Oregon attracts families for recreational fishing and many other outdoor activities. A hundred years ago, anyone fishing in the Diamond Lake was wasting their time, as the lake is naturally fishless. A waterfall prevents the natural migration of fish upstream from the waterway. In 1910, the Oregon Department of Fish and Wildlife (ODFW) Introduced fish into the lake and it soon became a profitable Rainbow Trout Fishery.

By the 1940’s the lake was not as profitable as the tui chub, a fish commonly used as a baitfish, was multiplying in the water. This fish, growing to about eight to twelve inches in length, is an omnivore and feeds on much the same diet as the rainbow trout. The fish breeds twice a year and without many predators quickly proves a serious competition for any other fish species.

It is not just as a competitive species that the tui chub causes harm to the introduced ecosystem of Diamond Lake but ultimately it harms the water quality. To maintain a healthy oxygenate water supply the invertebrate fauna of a lake, such as dragonfly nymphs, feeds on algae. The tui chub is a voracious feeder predating on the invertebrate life of lakes. In its healthy state, the lake contains well over 200 pounds of insects and other invertebrates such as leeches per acre. The tui chub reduced this to two pounds per acre. The remaining invertebrates are red worms capable of living in low oxygenated water.

In 1954, the ODFW dug a channel to enable them to lower the water level and then used the biodegradable poison rotenone to kill the water life in the lake. In addition to killing the chub and all other fish this poison kills all amphibian and invertebrate life within a lake. The insect life re-established itself allowing the ODFW to restock the lake with the rainbow trout and, once again, the lake became a popular fishery attracting 100,000 anglers a year to its waters.

In 1992, the tui chub again found its way into the waters of Diamond Lake. By 2003, the water quality was so bad that a toxic algal bloom caused the authorities to close the waters to swimmers. This combined with the decreased number of trout available to the fishermen impacted severely on the economy of the area.

The ODFW looked at methods for controlling the chub including the manual removal of the chub and the introduction of predictor species. Attempts at removal of the chub from Diamond Lake and other similar lakes, such as Lava Lake, were unsuccessful. There is concern that the introduction of predator fish causes concern to bio systems downstream from the lake for while no fish can migrate upstream the predators may swim downstream via the waterfall.

In 2006, the ODFW took the decision to poison the lake once again. Reopening the channel used in 1954, they lowered the level of the lake by eight feet effectively reducing its size by 20% an optimizing the poison’s capabilities. By 2007, the ODFW started restocking the lake with Rainbow Trout and now the clear waters of this mountain lake are again attracting anglers and others to its shores.

While the provision of a well-stocked healthy fishery, appears to be the main reason for the poisoning of Diamond Lake the main reason is the dollar. Recreational activities including fishing form the basis of many profitable businesses in the area. For that to function in the Diamond Lake area the lake had to be poisoned.