Lake Naivasha Report: Flower farms redeemed

By Macharia KamauUnusual environmental patterns caused the sudden death of fish in Lake Naivasha recently, an interim report has revealed.After on-spot measurements of dissolved oxygen, temperature and total dissolved solids in the lake, among other environmental parameters, the report says there was depression of oxygen levels in the water, due to unusual mixing associated with organic decomposition.The report, prepared during an Inter-Ministerial meeting held on Monday, further says big fish mostly died ‘due to the low surface area/volume ratio, which inhibited their ability to absorb oxygen at low levels’.About 700 fish died in Lake Naivasha due to lack of oxygen. Raw sewage was swept into the lake by floods, enriching it, and causing an algal boom that used up all the oxygen. [PHOTOs: FILE/STANDARD]Redeemed industryThe release of the report has redeemed the flower industry, which had been accused of causing the deaths of the fish by polluting the lake with pesticides. Had the claim been verified, international consumers could have boycotted Kenyan flower, dealing a severe big blow to the billion-shilling industry.And according to the experts, the fish have been dying due to lack of oxygen caused by the raw sewage swept into the lake by floods, which enriched the lake, causing an algal boom that used all the oxygen, which is needed for fish survival.Dr Stephen Mbithi, a marine expert had earlier said the depletion of dissolved oxygen was the most common cause of fish deaths in lakes."Oxygen depletion is either caused by a die-off of the microscopic green plants (phytoplankton) in ponds and lakes, or by overturns in which oxygen deficient water from the deeper levels of the pond mixes with water in the upper levels."He noted oxygen in the water must be above certain minimum concentrations for fish to survive. Mbithi who is also the chief executive officer of Fresh Produce Exporters Association of Kenya (FPEAK), said phytoplankton imparts a green colour to water in a properly fertilised pond."Phytoplankton is essential as part of the food chain and as a supplier of oxygen. But a sudden die-off of these plants may occur, especially during periods of cloudy, overcast weather, when the plants use more oxygen than they supply to the pond," he said."As the phytoplankton die and decompose, the remaining oxygen in the pond is consumed, and within a short time, a fish kill occurs due to oxygen depletion...and water colour also becomes brown" he addedHowever, Dr Mbithi said human activity and natural resources could also trigger algal blooms. "In rural areas for instance, agricultural run off from fields can wash fertiliser into the water. While in urban areas, nutrient sources, include treated wastewaters from septic systems, sewage treatment plants or urban storm water can run into the water, as happened during recent floods around lake Naivasha," said Dr Mbithi.The interim report released yesterday allays media speculations and statements from politicians, which accused flower firms around the lake, of polluting the lake by letting chemicals run into the lake.Possible causeWhile human activity around the lake may have caused the fish kills, pesticides have been ruled out as the possible cause."It is unlikely that pesticides were the main cause, as it would take several hundreds of drums of very toxic pesticide to increase the concentration of toxic pesticides in the lake to levels high enough to cause the number of kills we saw," said Dr Mbithi.The pectoral fins of a healthy fish points toward the tails, but the pectoral fins of a fish poisoned by insecticide curl up and point toward the head. However, ‘if organo-phosphate insecticide is the cause, the pectoral fins of the fish will be reversed which was not the case in the lake," he said.He said generally, in cases of poisoning, the small fish are killed first and all sizes of fish may die, but this was the opposite of what happened in lake Naivasha as the large fish died first, then the small ones later, he said.Statements from Nema indicate that the vast majority of fish, which died, had open mouths (indicating suffocation-lack of oxygen), and that large fish died first, followed by small fish. The statement also said that not all the lake was affected equally, most deaths appear in some areas of the lake.The reports of fish kills last month caused a major fallout in the multi-billion shilling flower industry as Kenya Flower Council (KFC) threatened to blacklist any member found to have contributed to the destruction in the bedrock of flower industry.Fishing banThe Government had also taken a flower company to court for alleged discharge of toxic waste into Lake Naivasha. And a ban had also been placed on fishing and hawking of fish along the lake.Public Health Minister Beth Mugo directed an immediate inspection of the flower firm to stop any more emission.

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Lake Naivasha Report: Flower farms redeemed

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