Today, six months from the day the Deepwater Horizon oil rig exploded 42 miles off the Louisiana shore, much is still unknown about the effects of the nation’s biggest oil spill, which gushed for 95 continuous days and spilled nearly 200 million barrels of oil into the Gulf of Mexico. (See a visual timeline of the oil spill.)

In early August, the U.S. National Oceanic and Atmospheric Administration (NOAA) released a report on the whereabouts of all the oil from the spill. Its report shows that half still remains in the Gulf, unable to be removed by burning or skimming—some of it in residual forms that are tough to extract or collect (tar balls, oil washing ashore, oil buried in sand or stuck in shore vegetation), some of it dispersed by chemicals, and some dispersed naturally.

No matter in what form, that oil still exists in the Gulf and still poses a grave threat to wildlife and the health of ecosystems. Most of the dispersed oil exists in microscopic droplets floating in the depths of the Gulf waters, which serve as a breeding grounds for much ocean life in an area scientists refer to as the "deep water column."

"We remain very concerned about the quarter of oil that was dispersed [chemically and naturally] and now exists in the deep water column," said NOAA head Jane Lubchenco on October 15. "These tiny droplets which are measured in parts per million or even parts per billion, though they are highly dispersed, doesn’t mean they are benign. They can still have very serious consequences for the small creatures and medium-sized creatures of the sea."

As of last week, 6,104 dead birds, 605 dead sea turtles and 95 dead mammals including dolphins have been collected in the impacted area. We haven’t even begun to see the long-term effects this oil has on the reproduction and survival of the more than 400 species that rely on Gulf Coast, or what those effects mean for Louisiana’s $2.4 billion-a-year fishing industry and $34 billion-a-year Gulf Coast tourism industry (in Louisiana, Alabama, Mississippi, and Florida). In total so far, the cost of the clean up is topping $11 billion, and number is quickly climbing. See oil spill by the numbers.

The immense amount of oil that spilled—19 times more than the Exxon Valdez spill—was treated with an equally unprecedented amount of chemical dispersants (nearly 2 million gallons). The chemical dispersant used, Corexit, contains toxic chemicals known to cause liver, kidney, and genetic damage, among other health problems. Its impacts on the Gulf—both immediate and long-term—remain a mystery to scientists and policymakers alike. "I’m amazed by how little science there is on the issue," said EPA Administrator Lisa Jackson in May.

For that reason, on Oct. 13, Earthjustice filed a petition on behalf of the Louisiana Shrimp Association, Florida Wildlife Federation, Gulf Restoration Network, the Alaska-based Cook Inletkeeper, Alaska Community Action on Toxics, Waterkeeper and Sierra Club asking the EPA to write rules that would set out exactly how and when dispersants could be used in the future. As Earthjustice attorney Marianne Engelman Lado explained:

Industry executives would like us to think that dispersants are some kind of fairy dust that magically removes oil from water. The fact is we have very little idea how toxic dispersants are, what quantities are safe to use or their long term effects on everything from people who work with the chemicals to coral in the water. We have little information about their long-term impact on life in the Gulf, or even whether the mix of oil and dispersants is more harmful than oil alone.

And while so much remains unknown, there are a few things we know for certain: Our government’s oversight over this industry was grossly negligent. We need much stronger oversight, we need much tighter regulations on offshore drilling, and we need to pay attention to science in the permitting of drilling projects. And when the science isn’t adequately supporting more or deeper drilling, we need to stop risking our economies, communities and ecosystems, and we need to stop drilling.

Earthjustice has been working in the courts to make sure that the kind of negligence that led to the Deepwater Horizon spill does not continue.

Before going into recess, the House of Representatives had been working on a legislative fix to some of the major problems within our offshore drilling industry and oversight. The House passed its offshore drilling reform bill, the CLEAR Act, in July. While this bill is not perfect, it is a huge improvement over our current systems, ensuring sound environmental reviews before oil companies can begin drilling, putting science back into the process of deciding where and when to drill, strengthening oil spill response plans, and engaging the National Oceanic and Atmospheric Administration in leasing.

The bill also holds oil companies responsible for the full costs of their spills, and reinvests money from oil and gas development into conservation and habitat restoration projects.

But in the time since the House passed the bill, the Obama administration lifted the moratorium on deep-sea drilling and reopened a huge portion of the Gulf to fishing, despite the lack of information supporting our ability to respond to another oil spill and a void of science on the effects of the dispersants on sea life.

This makes it even more crucial for the Senate to take up the House’s torch and address offshore drilling reform in the lame duck session after the mid-term elections. It is clear that we still desperately need to work to clean up that mess that is our offshore drilling industry and better protect our coastal environments and economies. We need the Senate to make passing a drilling reform bill its highest priority when it returns from recess. We cannot allow this kind of tragedy to happen again.

And we must not stop at just reforming our offshore drilling industry, either. We must understand that costs and damages of this tragedy are a part of the bigger picture of our nation’s dependence on dirty and harmful fossil fuels. It is time to get to work on ending this era of fossil fuel pollution and transitioning to a prosperous and safe clean energy economy.